"You know, I don't know if I'm allowed to say it, but we've got a really cool storyline with a Marvel character that appears on Castle this year," Lee said, according to IGN. "If you guys haven't seen the finale for Castle from this past season, it's extraordinary. [Castle creator] Andrew Marlow is really hitting his stride. And that was an underrated show that really found its momentum. And there's one episode, and I'm probably giving away a secret and I shouldn't because Andrew is going to kill me, with a Marvel superhero character."
Of course, Disney owns Marvel Comics, and is in the process of putting out movies and tv shows based off the Marvel library of over 5000 characters.
Marvel Comics is also putting out their own Castle graphic novel, Castle: Richard Castle’s Deadly Storm, written by Brian Michael Bendis and Kelly Sue DeConnick.
Speaking of Bendis, ABC is in the process of adapting AKA Jessica Jones for television. Makes sense that she might be the featured Marvel character.