Nope, it's not a joke. Martha Stewart is making an appearance in CastleVille in something called 'Martha's Kingdom,' which is just starting to roll out to players sometime this evening.
Above you see the loading screen with Martha's smiling avatar. I like how the sheep looks fearful of being shorn by Martha and turned into a hand woven bathroom rug. Below, Martha tweets about her first venture into social games, including the fact her game counterpart is very 'cute.' Cheeky.
Stay tuned for more information on Martha's Kingdom.