Given the boost in the spotlight — and cash flow — that comes with joining the cast of The Big Bang Theory, just about any actor would jump at the opportunity. But for Judd Hirsch, who plays the father of Leonard (Johnny Galecki), he had to be convinced.

TVGuide.com caught up with Hirsch at the Television Critics Association winter previews Monday, where he was promoting his upcoming CBS comedy Superior Donuts, and he told us the story about how he joined the cast.

And it all came down to one person: Galecki.

Superior Donuts won't be afraid to tackle hot button topics

"Would you like to be my father?" Hirsch remembers a shy Galecki asking him once when they were at an event celebrating James Burrows.

Hirsch — who does his best Galecki impression when retelling the story — also remembers Galecki saying he thought Leonard could easily be Hirsch's son because they are so similar.

Hirsch also lets us in on an inside Hollywood secret: what Galecki is really like in person.

Superior Donuts premieres Thursday, Feb. 2 at 8:30/7:30c on CBS. The Big Bang Theory airs Thursday nights at 8/7c, also on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)