Buffy the Vampire Slayer was a success for Joss Whedon but he recently revealed that his biggest regret was never having the chance to get the Buffy animated series off the ground.

"We got to do almost everything we wanted to do. The only thing we didn't get to do is an animated version, which was a delight for us because the writers themselves were working on it," Whedon said at a Director's Guild event, as quoted by The Huffington Post.

Many of the main cast members including Alyson Hannigan, Nicholas Brendon and Anthony Stewart Head returned to voice their characters, except Sarah Michelle Gellar, who was replaced by Giselle Loren, reports ScreenCrush. The animated series was also set during the first three seasons of Buffy.

"We wrote seven scripts … it was ‘what could we not do [on the regular series].’ They were really fun to write. We could not sell the show. We could not sell an animated Buffy, which I still find incomprehensible," Whedon continued.

Whedon is known for killing off fan-favorite characters as well, but he says the hardest Buffy character to kill was Buffy's mom, Joyce Summers.

Fans can check out the concept reel for the animated series below to see what could have been.