Playing Heroes of Might and Magic V on Ubisoft servers.

Hi everyone! Can someone help me? I have two licensed discs: one with the regular Heroes of Might and Magic V, and another with the Heroes of Might and Magic V: Tribes of the East expansion. But I seem to have lost the Tribes of the East disc. I only have the regular Heroes of Might and Magic V disc left. Will the key from my regular Heroes of Might and Magic V disc work in the Heroes of Might and Magic V: Tribes of the East game? Or can I only play the regular Heroes of Might and Magic V?