THE SIMPSONS: In the landmark 450th episode of THE SIMPSONS, the onstage and behind-the-scenes rapport between Krusty and his new female sidekick Princess Penelope (guest voice Anne Hathaway) grows in the all-new "Once Upon a Time in Springfield" episode of THE SIMPSONS airing Sunday, Jan. 10 (8:00-8:30 PM ET/PT) on FOX. THE SIMPSONS ™ and © 2009 TTCFFC ALL RIGHTS RESERVED. © 2009 FOX BROADCASTING CR: FOX

The Simpsons is celebrating its 20th year and 450th episode - and the voice of Bart Simpson, Nancy Cartwright, has been there every step of the way.

There was a time when few knew Cartwright could turn Bart on at will, but once it became common knowledge, the voice-over star fast became the party favor of choice.

Now, Cartwright is recognized nearly everywhere she goes and along with that notoriety comes the added burden of performing on demand.

Click onto video for details on friends and fan reactions once they learn Nancy Cartwright is the voice of Bart Simpson on The Simpsons.

The 450th episode ofThe Simpsons, titled Once Upon a Time in Springfield, airs Sunday, 8:00 p.m. ET/PT on Fox.

Afterward The Simpsons 20th Anniversary Special: in 3D on Ice! will air 8:30 p.m. ET/PT. It’s only fitting that Director Morgan Spurlock, famed Super Size Me documentary filmmaker, took the reigns to super size that tribute.