Find Out How Billy Bob Thornton Landed His Guest Star Role On 'The Big Bang Theory'

The Big Bang Theory is in its eighth season and it is still able to surprise us. When the comedy moved back to Thursday night, it brought with it a surprise guest star –– actor Billy Bob Thornton.

Unlike most guest stars on TV nowadays, The Big Bang Theory was able to keep Billy Bob's cameo undercover until the actual episode aired. He played Dr. Oliver Lorvis, an urologist who misreads Penny's (played by Kaley Cuoco-Sweeting) flirtation. So how did CBS keep it so hush-hush?

"A few months ago, we had seen an interview with Billy Bob talking about shows he likes. He was saying how much he likes Big Bang Theory, and watches it all the time, and gets so into it [that] he starts talking to the characters on the screen. We thought that was so cool, and we think he's so great," showrunner Steve Molaro told Entertainment Weekly.

In the episode, Dr. Oliver hits on Penny when she takes off her engagement ring while trying to boost her pharmaceutical sales. Despite knowing that they were going to keep it a secret, the network was shocked when the live-studio audience didn't spill the secret before the episode aired on Oct. 30.

"We knew that the network wasn't going to promote it, but there's only so much you can do, audience-wise. But somehow it stayed a secret. That was what we were hoping for, and it worked out well. People really responded to him and the episode," he told the publication.

Steve told The Hollywood Reporter that the onscreen chemistry between Billy Bob and the rest of the cast was due to the fact that everyone got along really well when they were filming.

"We would love to have him back. Obviously, he's a busy guy but he's told us he had a wonderful time," the hit comedy showrunner revealed to THR. "The cast, crew and writers, we all fell in love with that guy. He was a delight. It was the most fun, magical week having him around."