diff --git a/internal/gatewayapi/filters.go b/internal/gatewayapi/filters.go
index c31a322de5..5eed95aab6 100644
--- a/internal/gatewayapi/filters.go
+++ b/internal/gatewayapi/filters.go
@@ -210,6 +210,16 @@ func (t *Translator) ProcessGRPCFilters(
 		}
 	}
 
+	if httpFiltersContext.DirectResponse != nil && len(httpFiltersContext.Mirrors) > 0 {
+		httpFiltersContext.DirectResponse = nil
+		httpFiltersContext.Mirrors = nil
+
+		errs.Add(status.NewRouteStatusError(
+			errors.New(requestMirrorDirectResponseConflictMsg),
+			gwapiv1.RouteReasonIncompatibleFilters,
+		).WithType(gwapiv1.RouteConditionAccepted))
+	}
+
 	return httpFiltersContext, errs.GetAllErrors()
 }
 
diff --git a/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.in.yaml b/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.in.yaml
new file mode 100644
index 0000000000..155d42ae5e
--- /dev/null
+++ b/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.in.yaml
@@ -0,0 +1,58 @@
+gateways:
+  - apiVersion: gateway.networking.k8s.io/v1
+    kind: Gateway
+    metadata:
+      namespace: envoy-gateway
+      name: gateway-1
+    spec:
+      gatewayClassName: envoy-gateway-class
+      listeners:
+        - name: http
+          protocol: HTTP
+          port: 80
+          allowedRoutes:
+            namespaces:
+              from: All
+grpcRoutes:
+  - apiVersion: gateway.networking.k8s.io/v1
+    kind: GRPCRoute
+    metadata:
+      namespace: default
+      name: mirror-direct-response
+    spec:
+      parentRefs:
+        - namespace: envoy-gateway
+          name: gateway-1
+          sectionName: http
+      rules:
+        - backendRefs:
+            - name: service-1
+              port: 8080
+          filters:
+            - type: RequestMirror
+              requestMirror:
+                backendRef:
+                  kind: Service
+                  name: service-1
+                  port: 8080
+            - type: ExtensionRef
+              extensionRef:
+                group: gateway.envoyproxy.io
+                kind: HTTPRouteFilter
+                name: mirror-direct-response
+        - backendRefs:
+            - name: service-2
+              port: 8080
+httpFilters:
+  - apiVersion: gateway.envoyproxy.io/v1alpha1
+    kind: HTTPRouteFilter
+    metadata:
+      name: mirror-direct-response
+      namespace: default
+    spec:
+      directResponse:
+        statusCode: 404
+        contentType: text/plain
+        body:
+          type: Inline
+          inline: "blocked"
diff --git a/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.out.yaml b/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.out.yaml
new file mode 100644
index 0000000000..798bd83c26
--- /dev/null
+++ b/internal/gatewayapi/testdata/grpcroute-with-conflicting-filters.out.yaml
@@ -0,0 +1,199 @@
+gateways:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: Gateway
+  metadata:
+    name: gateway-1
+    namespace: envoy-gateway
+  spec:
+    gatewayClassName: envoy-gateway-class
+    listeners:
+    - allowedRoutes:
+        namespaces:
+          from: All
+      name: http
+      port: 80
+      protocol: HTTP
+  status:
+    listeners:
+    - attachedRoutes: 1
+      conditions:
+      - lastTransitionTime: null
+        message: Sending translated listener configuration to the data plane
+        reason: Programmed
+        status: "True"
+        type: Programmed
+      - lastTransitionTime: null
+        message: Listener has been successfully translated
+        reason: Accepted
+        status: "True"
+        type: Accepted
+      - lastTransitionTime: null
+        message: Listener references have been resolved
+        reason: ResolvedRefs
+        status: "True"
+        type: ResolvedRefs
+      name: http
+      supportedKinds:
+      - group: gateway.networking.k8s.io
+        kind: HTTPRoute
+      - group: gateway.networking.k8s.io
+        kind: GRPCRoute
+grpcRoutes:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: GRPCRoute
+  metadata:
+    name: mirror-direct-response
+    namespace: default
+  spec:
+    parentRefs:
+    - name: gateway-1
+      namespace: envoy-gateway
+      sectionName: http
+    rules:
+    - backendRefs:
+      - name: service-1
+        port: 8080
+      filters:
+      - requestMirror:
+          backendRef:
+            kind: Service
+            name: service-1
+            port: 8080
+        type: RequestMirror
+      - extensionRef:
+          group: gateway.envoyproxy.io
+          kind: HTTPRouteFilter
+          name: mirror-direct-response
+        type: ExtensionRef
+    - backendRefs:
+      - name: service-2
+        port: 8080
+  status:
+    parents:
+    - conditions:
+      - lastTransitionTime: null
+        message: Route is accepted
+        reason: Accepted
+        status: "True"
+        type: Accepted
+      - lastTransitionTime: null
+        message: |-
+          Dropped Rule(s) [0]: Invalid filter ExtensionRef: unknown kind gateway.envoyproxy.io/HTTPRouteFilter.
+          RequestMirror filter cannot be used when the rule also configures a DirectResponse filter.
+        reason: IncompatibleFilters, UnsupportedValue
+        status: "True"
+        type: PartiallyInvalid
+      - lastTransitionTime: null
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
+        type: ResolvedRefs
+      controllerName: gateway.envoyproxy.io/gatewayclass-controller
+      parentRef:
+        name: gateway-1
+        namespace: envoy-gateway
+        sectionName: http
+infraIR:
+  envoy-gateway/gateway-1:
+    proxy:
+      listeners:
+      - name: envoy-gateway/gateway-1/http
+        ports:
+        - containerPort: 10080
+          name: http-80
+          protocol: HTTP
+          servicePort: 80
+      metadata:
+        labels:
+          gateway.envoyproxy.io/owning-gateway-name: gateway-1
+          gateway.envoyproxy.io/owning-gateway-namespace: envoy-gateway
+        ownerReference:
+          kind: GatewayClass
+          name: envoy-gateway-class
+      name: envoy-gateway/gateway-1
+      namespace: envoy-gateway-system
+xdsIR:
+  envoy-gateway/gateway-1:
+    accessLog:
+      json:
+      - path: /dev/stdout
+    globalResources:
+      proxyServiceCluster:
+        metadata:
+          kind: Service
+          name: envoy-envoy-gateway-gateway-1-196ae069
+          namespace: envoy-gateway-system
+          sectionName: "8080"
+        name: envoy-gateway/gateway-1
+        settings:
+        - addressType: IP
+          endpoints:
+          - host: 7.6.5.4
+            port: 8080
+            zone: zone1
+          metadata:
+            kind: Service
+            name: envoy-envoy-gateway-gateway-1-196ae069
+            namespace: envoy-gateway-system
+            sectionName: "8080"
+          name: envoy-gateway/gateway-1
+          protocol: TCP
+    http:
+    - address: 0.0.0.0
+      externalPort: 80
+      grpc:
+        enableGRPCStats: true
+        enableGRPCWeb: true
+      hostnames:
+      - '*'
+      metadata:
+        kind: Gateway
+        name: gateway-1
+        namespace: envoy-gateway
+        sectionName: http
+      name: envoy-gateway/gateway-1/http
+      path:
+        escapedSlashesAction: UnescapeAndRedirect
+        mergeSlashes: true
+      port: 10080
+      routes:
+      - directResponse:
+          statusCode: 500
+        hostname: '*'
+        isHTTP2: true
+        metadata:
+          kind: GRPCRoute
+          name: mirror-direct-response
+          namespace: default
+        name: grpcroute/default/mirror-direct-response/rule/0/match/-1/*
+      - destination:
+          metadata:
+            kind: GRPCRoute
+            name: mirror-direct-response
+            namespace: default
+          name: grpcroute/default/mirror-direct-response/rule/1
+          settings:
+          - addressType: IP
+            endpoints:
+            - host: 7.7.7.7
+              port: 8080
+            metadata:
+              kind: Service
+              name: service-2
+              namespace: default
+              sectionName: "8080"
+            name: grpcroute/default/mirror-direct-response/rule/1/backend/0
+            protocol: GRPC
+            weight: 1
+        hostname: '*'
+        isHTTP2: true
+        metadata:
+          kind: GRPCRoute
+          name: mirror-direct-response
+          namespace: default
+        name: grpcroute/default/mirror-direct-response/rule/1/match/-1/*
+    readyListener:
+      address: 0.0.0.0
+      ipFamily: IPv4
+      path: /ready
+      port: 19003
diff --git a/internal/provider/kubernetes/indexers.go b/internal/provider/kubernetes/indexers.go
index 52e50d459e..ef3cedb017 100644
--- a/internal/provider/kubernetes/indexers.go
+++ b/internal/provider/kubernetes/indexers.go
@@ -466,6 +466,21 @@ func backendGRPCRouteIndexFunc(rawObj client.Object) []string {
 				)
 			}
 		}
+
+		for _, filter := range rule.Filters {
+			if filter.Type != gwapiv1.GRPCRouteFilterRequestMirror {
+				continue
+			}
+
+			mirrorBackendRef := filter.RequestMirror.BackendRef
+
+			backendRefs = append(backendRefs,
+				types.NamespacedName{
+					Namespace: gatewayapi.NamespaceDerefOr(mirrorBackendRef.Namespace, grpcroute.Namespace),
+					Name:      string(mirrorBackendRef.Name),
+				}.String(),
+			)
+		}
 	}
 	return backendRefs
 }
diff --git a/internal/provider/kubernetes/indexers_test.go b/internal/provider/kubernetes/indexers_test.go
new file mode 100644
index 0000000000..a09b9f1f64
--- /dev/null
+++ b/internal/provider/kubernetes/indexers_test.go
@@ -0,0 +1,247 @@
+// Copyright Envoy Gateway Authors
+// SPDX-License-Identifier: Apache-2.0
+// The full text of the Apache license is available in the LICENSE file at
+// the root of the repo.
+
+package kubernetes
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/utils/ptr"
+	gwapiv1 "sigs.k8s.io/gateway-api/apis/v1"
+
+	egv1a1 "github.com/envoyproxy/gateway/api/v1alpha1"
+)
+
+func TestBackendGRPCRouteIndexFunc(t *testing.T) {
+	testCases := []struct {
+		name     string
+		route    *gwapiv1.GRPCRoute
+		expected []string
+	}{
+		{
+			name: "no filters, single backend",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-1",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Name: "service-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/service-1"},
+		},
+		{
+			name: "request mirror filter includes mirror backendRef",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-mirror",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Name: "service-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+							Filters: []gwapiv1.GRPCRouteFilter{
+								{
+									Type: gwapiv1.GRPCRouteFilterRequestMirror,
+									RequestMirror: &gwapiv1.HTTPRequestMirrorFilter{
+										BackendRef: gwapiv1.BackendObjectReference{
+											Kind: ptr.To(gwapiv1.Kind("Service")),
+											Name: "mirror-service",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/service-1", "default/mirror-service"},
+		},
+		{
+			name: "mirror filter with cross-namespace backendRef",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-cross-ns",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Name: "service-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+							Filters: []gwapiv1.GRPCRouteFilter{
+								{
+									Type: gwapiv1.GRPCRouteFilterRequestMirror,
+									RequestMirror: &gwapiv1.HTTPRequestMirrorFilter{
+										BackendRef: gwapiv1.BackendObjectReference{
+											Kind:      ptr.To(gwapiv1.Kind("Service")),
+											Namespace: ptr.To(gwapiv1.Namespace("other-ns")),
+											Name:      "mirror-service",
+											Port:      ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/service-1", "other-ns/mirror-service"},
+		},
+		{
+			name: "multiple mirror filters in same rule",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-multi-mirror",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Name: "service-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+							Filters: []gwapiv1.GRPCRouteFilter{
+								{
+									Type: gwapiv1.GRPCRouteFilterRequestMirror,
+									RequestMirror: &gwapiv1.HTTPRequestMirrorFilter{
+										BackendRef: gwapiv1.BackendObjectReference{
+											Kind: ptr.To(gwapiv1.Kind("Service")),
+											Name: "mirror-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+								{
+									Type: gwapiv1.GRPCRouteFilterRequestMirror,
+									RequestMirror: &gwapiv1.HTTPRequestMirrorFilter{
+										BackendRef: gwapiv1.BackendObjectReference{
+											Kind: ptr.To(gwapiv1.Kind("Service")),
+											Name: "mirror-2",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/service-1", "default/mirror-1", "default/mirror-2"},
+		},
+		{
+			name: "non-mirror filter is ignored",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-header-filter",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Name: "service-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+							Filters: []gwapiv1.GRPCRouteFilter{
+								{
+									Type: gwapiv1.GRPCRouteFilterRequestHeaderModifier,
+									RequestHeaderModifier: &gwapiv1.HTTPHeaderFilter{
+										Set: []gwapiv1.HTTPHeader{
+											{Name: "x-custom", Value: "value"},
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/service-1"},
+		},
+		{
+			name: "backend with Backend kind is indexed",
+			route: &gwapiv1.GRPCRoute{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "grpcroute-backend-kind",
+					Namespace: "default",
+				},
+				Spec: gwapiv1.GRPCRouteSpec{
+					Rules: []gwapiv1.GRPCRouteRule{
+						{
+							BackendRefs: []gwapiv1.GRPCBackendRef{
+								{
+									BackendRef: gwapiv1.BackendRef{
+										BackendObjectReference: gwapiv1.BackendObjectReference{
+											Kind: ptr.To(gwapiv1.Kind(egv1a1.KindBackend)),
+											Name: "backend-1",
+											Port: ptr.To(gwapiv1.PortNumber(8080)),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: []string{"default/backend-1"},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			result := backendGRPCRouteIndexFunc(tc.route)
+			require.ElementsMatch(t, tc.expected, result)
+		})
+	}
+}
diff --git a/release-notes/current.yaml b/release-notes/current.yaml
index 871764e8e4..4a5d170f29 100644
--- a/release-notes/current.yaml
+++ b/release-notes/current.yaml
@@ -50,6 +50,8 @@ bug fixes: |
   Made ConnectionLimit.Value optional so users can configure MaxConnectionDuration, MaxRequestsPerConnection, or MaxStreamDuration without setting a max connections value.
   Fixed endpoint hostname is not respected when doing active health check.
   Fixed ratelimit deployment missing metrics container port (19001), which prevented PodMonitor/ServiceMonitor from targeting the metrics endpoint.
+  Fixed GRPCRoute RequestMirror filter backend not being indexed, causing "service not found" errors for mirror targets that exist in the cluster.
+  Fixed GRPCRoute not detecting conflicting RequestMirror and DirectResponse filters, which caused the mirror to be silently dropped.
   Fixed per-endpoint hostname override not working because the auto-generated wildcard hostname.
 
 # Enhancements that improve performance.