The former "Happy Days" star tells ET's Jann Carl why she made an appearance on Scott Baio's VH1 series.

It's hard to believe, but it's been 24 years since "Joanie Loves Chachi" went off the air, so when SCOTT BAIO, who played Chachi, invited ERIN MORAN, who was Joanie, to guest on his VH1 series, "Scott Baio is 45 ... and Single," this past summer, she was a little reluctant.

"The producers called me and asked me, and I said, 'No, you're going to have to get Scott to call me, and he can tell a good reason,'" Erin tells ET's JANN CARL. "He called me and he gave me the lowdown, so I said, 'Okay, as long as you don't make me look bad, then I will do it. I am absolutely there for you.' "

Scott stuck to his promise, so Erin, who admits she isn't crazy about reality TV, did the show this past summer and has been getting a really positive reaction from the fans, with comments such as: "I'm so glad you were like that with him. Good for you."

Erin, who has been with her second husband for 14 years, says she has the perfect advice for her former co-star: "Just stick with it and stay monogamous. You've done it to death, Scott, with women up the yin-yang. I think it's time to be one-on-one."

Erin also tells Jann that if you are friends first, and remain friends, it is easier to stick through thick and thin.

"My husband and I have gotten closer and closer, and just laugh," she says. "We can be together 24 hours a day and not be sick of each other."