This is not how I imagined an interview with Kenan Thompson should go. Worn out from a long day of interviews and autographing to promote his latest movie, Fat Albert, the normally effervescent, over-the-top young comedian who played such indelible Nickelodeon roles as Super Dude, Pierre Escargot and the bumbling employee of Good Burger, just does not have the energy for his trademark Bill Cosby impressions.

But even if the actor is not on his A game, he still expresses a genuine personal interest rare in the press junket crowd. Not only has he remembered my full name off his itinerary, he immediately starts engaging me in conversation about how difficult it was to get into Harvard, jokingly speculating about his own chances of acceptance at the college.

Thompson, who began his career on the comedic sketch show “All That” and the sitcom “Kenan and Kel” on Nickelodeon, is now a regular member on “Saturday Night Live” (SNL) and can be found in the movies Barbershop 2 and Love Don’t Cost a Thing.

It is nearly impossible to mention Thompson without thinking of Kel Mitchell, his former television co-star. Years after collaborating together on Nickelodeon, the two are still friends, yet pursing separate career paths; Kel is on the new show “Dance 360.” “We’re not really working together right now, because we want to establish the fact there is a Kenan Thompson and a Kel Mitchell.”

For his newest step towards establishing himself as a solo performer, Thompson has, to be boldly cliché, big shoes to fill as the title role of the live-action movie, Fat Albert. The movie is based on iconic comedian Bill Cosby’s hit 1970s cartoon series “Fat Albert and the Cosby Kids,” which is, itself, based off of Cosby’s standup routine about his childhood. Directed by Joel Zwick (coming off aptly enough from the high of another “fat” movie, My Big Fat Greek Wedding) and produced by Cosby, who also co-wrote the script with Charles Kipps, the problem-solving “big guy with the big heart” will get his own movie this Christmas.

Surprisingly, Thompson was not the original actor cast as Fat Albert, nor was it thought that the project would ever be completed after Cosby and original director Forest Whitaker fell apart over creative differences in 2002.

When recounting how he became a part of this movie, Thompson describes his first audition as the “biggest misunderstanding in the world.” Having been given his lines just that morning, his audition was ill-prepared and read cold. Thompson was angry and shocked after being informed his audition was terrible and being publicly thrown out of the room.

Calling his manager, who had once represented Whitaker, Thompson was able to secure a second, more favorable audition. The second time around, final casting for the role of Fat Albert came down to Thompson and Omar Benson Miller (8 Mile, Sorority Boys), with the part eventually going to the latter. Thompson explains that Fat Albert is the biggest and tallest member of his gang, and that Miller, who stands at 6’5”, is easily the larger of the two.

But when Zwick came aboard, the audition process began once again.

Thompson remembers how he made a special audition tape for Cosby. “The legend is that [Cosby] watched, like, twenty seconds of it and just gave me the job,” says the Fat Albert star.

On “the Cos,” his nickname for Bill Cosby, Thompson is full of praise; he gushed about how surreal it was to work with his hero.

“I mean, I saw him yesterday, but I don’t believe it,” says Thompson. “I’ve been watching Bill Cosby all my life, he’s the main person, the first comic who I really identified with because I couldn’t watch Eddie Murphy, I couldn’t watch Richard Pryor growing up, so really all I had was Bill Cosby.”

Thompson adds that Cosby, “told me that I was a blessing to him, so I thought that was very sweet of him; I made a new friend.”

Cosby, who voiced many of the characters in the Fat Albert cartoon, gave Thompson relative freedom with personalizing characterization: he did not even coach on how to deliver the Albert tagline, “Hey, hey, hey, it’s Fat Albert.”

“I know that Fat Albert is a clean thing, and it’s a Cosby thing, and I wouldn’t want to do anything to tarnish it, but I want also to be free to do whatever is funny for me,” says Thompson.