diff --git a/dotnet/src/AutoGen.Core/Extension/GroupChatExtension.cs b/dotnet/src/AutoGen.Core/Extension/GroupChatExtension.cs
index a5009e211556..6b17a2b93fd6 100644
--- a/dotnet/src/AutoGen.Core/Extension/GroupChatExtension.cs
+++ b/dotnet/src/AutoGen.Core/Extension/GroupChatExtension.cs
@@ -51,7 +51,10 @@ public static async IAsyncEnumerable<IMessage> SendAsync(
                 yield break;
             }
 
-            chatHistory = messages;
+            // messages will contain the complete chat history, include initalize messages
+            // but we only need to add the last message to the chat history
+            // fix #3268
+            chatHistory = chatHistory.Append(lastMessage);
         }
     }
 
diff --git a/dotnet/test/AutoGen.Tests/GroupChat/GroupChatTests.cs b/dotnet/test/AutoGen.Tests/GroupChat/GroupChatTests.cs
index 7a7a27be9b10..19ca02ae92fa 100644
--- a/dotnet/test/AutoGen.Tests/GroupChat/GroupChatTests.cs
+++ b/dotnet/test/AutoGen.Tests/GroupChat/GroupChatTests.cs
@@ -4,8 +4,10 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using FluentAssertions;
+using Moq;
 using Xunit;
 
 namespace AutoGen.Tests;
@@ -51,4 +53,36 @@ public async Task ItTerminateConversationWhenAgentReturnTerminateKeyWord()
         chatHistory.Count().Should().Be(3);
         chatHistory.Last().From.Should().Be("Cathy");
     }
+
+    [Fact]
+    public async Task ItSendAsyncDoesntAddDuplicateInitializeMessagesTest()
+    {
+        // fix #3268
+        var alice = new DefaultReplyAgent("Alice", "I am alice");
+        var bob = new DefaultReplyAgent("Bob", "I am bob");
+        var cathy = new DefaultReplyAgent("Cathy", $"I am cathy, {GroupChatExtension.TERMINATE}");
+
+        var roundRobinOrchestrator = new RoundRobinOrchestrator();
+        var orchestrator = Mock.Of<IOrchestrator>();
+        Mock.Get(orchestrator).Setup(x => x.GetNextSpeakerAsync(It.IsAny<OrchestrationContext>(), It.IsAny<CancellationToken>()))
+            .Returns((OrchestrationContext context, CancellationToken token) =>
+            {
+                // determine if initialize message is already sent and not added twice
+                context.ChatHistory.Where(x => x.From == alice.Name).Count().Should().Be(1);
+
+                return roundRobinOrchestrator.GetNextSpeakerAsync(context, token);
+            });
+
+        var groupChat = new GroupChat([alice, bob, cathy], orchestrator);
+        groupChat.AddInitializeMessage(new TextMessage(Role.User, "Hello", from: alice.Name));
+
+        var maxRound = 2;
+        var chatHistory = new List<IMessage>();
+        await foreach (var message in groupChat.SendAsync(chatHistory, maxRound))
+        {
+            chatHistory.Add(message);
+        }
+
+        chatHistory.Count().Should().Be(2);
+    }
 }