If you haven't watched the latest episodes of Adventure Time you might not now Princess Bubblegum is now 13, which is Finn's age.
The new episode Heat Signature is out today, if you watch the episode "Videomakers" the film they didn't show was Heat Signature 3. Maybe, the writers just like the title. This is also the only new episode till June 6th when Season 3 starts.
Here's some more "the Lich" or lich king stuff. Below is a impressive sketch of the lich holding PB and Finn about to start something, with some more lich art.