'Happy Days' Actor Anson Williams Shares Secrets of the Show

— -- A lot has been said about "Happy Days" in the 30 years that it's been off the air.

However, Anson Williams, who played Potsie Weber in the series, still has stories to tell. In his new book, "Singing to a Bulldog: From 'Happy Days' to Hollywood Director, and the Unlikely Mentor Who Got Me There," Williams, 65, dishes on his life in Hollywood and lessons he's learned throughout his career -- and yes, "Happy Days" was a big part of that.

To celebrate his book's release on Tuesday, Williams told ABC News five secrets about his time with Richie and the Fonz. Here they are, in his words, below:

1. Robin Williams was not originally cast to be Mork from Ork. The original actor quit and walked off the set two days before the show taped in front of a live audience. Al Molinaro suggested Robin from his Improv class and a star was born!

2. Two Beatles visited the "Happy Days" set. John Lennon brought his son Julian to spend the day watching us rehearse and, later, Ringo Starr paid a visit.

3. Tom Bosley and Erin Moran were not the original Mr. Cunningham and Joanie Cunningham. Two other actors were cast for the first pilot, which aired on an episode of "Love American Style."

4. The original "Happy Days" pilot aired before the movie "American Graffiti" and wasn't picked up. After the success of the movie, another pilot was shot and it was picked up. The show ran for 10 years.

5. All the regular cast members had to audition and prove they could play softball, per [series creator] Garry Marshall. Henry Winkler wasn't a regular cast member at the start, so later we had to teach him to play the game.