NEW YORK (AP) - Jason Ritter says working with Lauren Graham on NBC's "Parenthood" is "one of the greatest experiences" of his life.
"Parenthood," which airs Tuesdays (10 p.m. EDT), is in its fourth season, and Ritter's character, Mark, is engaged to Graham's character, Sarah.
"I remember I was really nervous before I started working with her," Ritter said in a recent interview. "You can fake liking each other and having a relationship but it's very difficult for me. It's much easier if you have some kind of ground level of just liking each other, and so I was really relieved when we got along, and it's just been so fun and I feel like I've learned so much. She's so fast and funny and I'm constantly just like trying to keep up with her."
Ritter, 32, was introduced in the first season of "Parenthood" for a three-episode arc. It was written that he would date Sarah but they would soon break up, but the show's producers and writers were so impressed with Ritter's performance, they kept writing him into episodes. He left to star in the 2010 TV drama "The Event," but they brought him back after that show was canceled.
"They just kept on sort of bringing me back," Ritter said. "First of all, I love working on that show so much. I have such a fun time, and it's so exciting and inspiring to act opposite Lauren. She's just so fun to work with and, plus, you know, in the second season, I was getting jealous of her other ('Parenthood') boyfriends."
There's a lot to keep up with working on "Parenthood." Ritter says the actors are free to ad-lib or make changes to the dialogue. Sometimes the characters talk over each other just as people often do in real life.
"Because you don't necessarily know what someone else is going to say, it keeps you on your toes and in the moment because you can't necessarily count on anything," Ritter said.
Ritter says he's not sure whether Mark's relationship with Sarah will last or whether he'll be around for the entire season.
He does have other work, voicing a character on the Disney animated show "Gravity Falls." He grew up loving cartoons and recalls his parents taking him to animation festivals. (His father is the late John Ritter, who played Jack Tripper on "Three's Company.")
"I really enjoyed 'He-Man' and 'She-Ra: Princess of Power,'" he laughed. "'Teenage Mutant Ninja Turtles' was one that I would watch like before I would go to school in the morning, like eat breakfast and watch that. I also watched the entire Disney afternoon lineup. I think it was "TaleSpin," ''DuckTales," ''Chip 'n' Dale Rescue Rangers" and "Darkwing Duck." I watched all four of those. For two hours. When I got home."