diff --git a/include/game/game_handler.hpp b/include/game/game_handler.hpp
index 31e839ec..e272dd17 100644
--- a/include/game/game_handler.hpp
+++ b/include/game/game_handler.hpp
@@ -134,7 +134,8 @@ public:
                  uint16_t port,
                  const std::vector<uint8_t>& sessionKey,
                  const std::string& accountName,
-                 uint32_t build = 12340);
+                 uint32_t build = 12340,
+                 uint32_t realmId = 0);
 
     /**
      * Disconnect from world server
@@ -957,6 +958,7 @@ private:
     std::vector<uint8_t> sessionKey;    // 40-byte session key from auth server
     std::string accountName;             // Account name
     uint32_t build = 12340;              // Client build (3.3.5a)
+    uint32_t realmId_ = 0;               // Realm ID from auth REALM_LIST (used in WotLK AUTH_SESSION)
     uint32_t clientSeed = 0;             // Random seed generated by client
     uint32_t serverSeed = 0;             // Seed from SMSG_AUTH_CHALLENGE
 
diff --git a/src/core/application.cpp b/src/core/application.cpp
index 9295733f..d2cbb521 100644
--- a/src/core/application.cpp
+++ b/src/core/application.cpp
@@ -892,12 +892,25 @@ void Application::setupUICallbacks() {
             accountName = "TESTACCOUNT";
         }
 
+        uint32_t realmId = 0;
+        {
+            // WotLK AUTH_SESSION includes a RealmID field; some servers reject if it's wrong/zero.
+            const auto& realms = authHandler->getRealms();
+            for (const auto& r : realms) {
+                if (r.name == realmName && r.address == realmAddress) {
+                    realmId = r.id;
+                    break;
+                }
+            }
+            LOG_INFO("Selected realmId=", realmId);
+        }
+
         uint32_t clientBuild = 12340; // default WotLK
         if (expansionRegistry_) {
             auto* profile = expansionRegistry_->getActive();
             if (profile) clientBuild = profile->build;
         }
-        if (gameHandler->connect(host, port, sessionKey, accountName, clientBuild)) {
+        if (gameHandler->connect(host, port, sessionKey, accountName, clientBuild, realmId)) {
             LOG_INFO("Connected to world server, transitioning to character selection");
             setState(AppState::CHARACTER_SELECTION);
         } else {
diff --git a/src/game/game_handler.cpp b/src/game/game_handler.cpp
index a56d955f..0a95725a 100644
--- a/src/game/game_handler.cpp
+++ b/src/game/game_handler.cpp
@@ -114,7 +114,8 @@ bool GameHandler::connect(const std::string& host,
                           uint16_t port,
                           const std::vector<uint8_t>& sessionKey,
                           const std::string& accountName,
-                          uint32_t build) {
+                          uint32_t build,
+                          uint32_t realmId) {
 
     if (sessionKey.size() != 40) {
         LOG_ERROR("Invalid session key size: ", sessionKey.size(), " (expected 40)");
@@ -134,6 +135,7 @@ bool GameHandler::connect(const std::string& host,
     this->sessionKey = sessionKey;
     this->accountName = accountName;
     this->build = build;
+    this->realmId_ = realmId;
     requiresWarden_ = false;
     wardenGateSeen_ = false;
     wardenGateElapsed_ = 0.0f;
@@ -1433,7 +1435,8 @@ void GameHandler::sendAuthSession() {
         accountName,
         clientSeed,
         sessionKey,
-        serverSeed
+        serverSeed,
+        realmId_
     );
 
     LOG_DEBUG("CMSG_AUTH_SESSION packet size: ", packet.getSize(), " bytes");