Ninety-year-old Dick Van Dyke has had a lengthy career in television, theater and film, but out of all of the projects he's been a part of -- "Mary Poppins," "Bye Bye Birdie," "Diagnosis: Murder," "The Dick Van Dyke Show," "Chitty Chitty Bang Bang," to name a few -- one of them continues to stand out among the rest .

"The five years at 'The Dick Van Dyke Show' were the happiest five years in all of our lives," Van Dyke tells "Oprah: Where Are They Now?" in the above clip. "It was creative, we laughed and joked every day, and there was a lot of improv going on. It was just such fun to do."

One of Van Dyke's costars on "The Dick Van Dyke Show" was then-23-year-old Mary Tyler Moore. Upon first meeting Moore, Van Dyke admits that he had some concerns about her playing his wife on the show.

"She was just beautiful, but I thought she was a little young," Van Dyke explains. "She had this strange mid-Atlantic accent, kind of like Katherine Hepburn. I said, 'Well, she's as cute as she can be, but can she do comedy?'"

Indeed she could, which Van Dyke quickly learned.

"It wasn't, I don't think, two episodes before her timing came," he says. "She got it like that, and what a pleasure."

In fact, Van Dyke adds, he and Moore actually developed quite the mutual fondness.

"We had like a teenage crush on each other," he says, smiling. "It was fun."

"The Dick Van Dyke Show" debuted on CBS in 1961, and ran for five years, airing its final episode 50 years ago on June 1, 1966.

"I hated to see it go," Van Dyke says. "I'd still be doing it if they let me!"

Another candid clip with the actor:

Inside Dick Van Dyke's marriage to a woman 46 years his junior