Actually, the stamps themselves are the same, but the cover is different.
And here is the press release from Royal Mail (PDF).
And here is another first day cover, this time from Bletchley Park (which some of you might know from the WW2 code-breaking efforts), highlighting Tudor spymasters and code breakers. The first day covers are available from the Bletchley Park post office. Proceeds will go to the Bletchley Park preservation fund. You can get more info from the press release here (PDF).