To be honest, if ArenaNet had announced that the eighth and final profession for Guild Wars 2 was anything but the Mesmer, there would have been worldwide riots. Fortunately, such is not the case, as the studio confirmed in a brief tweet that the Mesmer would be the last addition to the class roster.
According to the tweet, the full reveal of the Mesmer was slated for Wednesday, but the CMs said that "someone jumped the gun" and let the information slip earlier than desired. Apparently GameReactor Denmark jumped the embargo and posted a video about the reveal (the video has since been removed from the site).
We'll be waiting for the official unveiling with bated breath!