The concept here is that the characters are actors working on the show. Their real names are based on their actors' names.
Since the show's premiere, I've spoken with the characters during breaks in filming. They are a friendly sort (The Lich is a really nice guy), and are always honest with me.
Frost & Fire
Jessica (the actress who plays Flame Princess, and played Young PB) spoke to me while filming her next appearance:
To my loyal fans: this quote-on-quote (sic) break-up was not my descision. I had been waiting a long time to be on screen with my boyfriend again after I played Young PB in "Mortal Recoil" and "Too Young". I'm as angry as you are, and have submitted a complaint to Mr. Ward. I truly love Finn, and have before my first day on set for the ending of "Mortal Recoil". This whole thing has extremely disgruntled me. First I get re-supplanted by the actress I supplanted in the first place, then this! Rest assured, folks, FP and Finn will get back together. I haven't been told when, but I can feel it. Our character's were so happy together, and me and Finn are happy together. Thank you all for your support through this period of uncertainty.
Jeremy (Finn's actor) also told me this:
I can't tell you how mad I am right now. That last scene in "Frost & Fire" was one of the hardest scenes I had to do, and took 8 takes. Me and Jessica [Actress of Flame Princess and Young PB] are angry about the descision to break us up. Now I'm having to go back to Princess Bubblegum in "Too Old", and me and her have had a strained relationship as of late off-set. So to act affectionate with her again is extremely uncomfortable. But I have a feeling Finn and Flame Princess will get back together, so don't fear...or DDoS me, because I'd never act like I did in the episode.
More interviews coming soon!