"The Big Bang Theory" brought on a ton of incredible guest stars throughout its 12-season run -- including a ton of actors from the "Star Trek" franchise alone -- but one of the most exciting cameos had to be courtesy of Mark Hamill, the man famous for playing Luke Skywalker in "Star Wars" who appeared in the season 11 episode "The Bow Tie Asymmetry." According to a tell-all book about the show, though, he has one huge regret about his appearance on the series.

Hamill, playing himself, ends up encountering Howard Wolowitz (Simon Helberg) after Howard finds Hamill's lost dog, appropriately named "Bark Hamill" -- and then offers Howard a favor. Howard gleefully cashes in on that favor by getting Hamill to officiate the wedding of his friends Sheldon Cooper (Jim Parsons) and Amy Farrah Fowler (Mayim Bialik) ... but as Hamill told Jessica Radloff in her book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," he was pretty unfamiliar with the series itself for a while.

"I didn't really stick with the series early on," Hamill admitted, saying that he actually got back into it while filming "The Last Jedi" in England. "I would have to do the treadmill, and I would notice on Saturdays and Sundays, one of the TV stations would air four-hour blocks of 'Big Bang,' he continued. "By that time, there were so many episodes I had not seen, so I would do the treadmill and measure them in, 'Well, I'll do one episode's worth on the treadmill.' And then, 'Oh, I'll do two episodes' worth on the treadmill,' followed by three." When all was said and done, Hamill said he had probably seen somewhere around 30-40 episodes before he guest-starred on the series but wished he had seen more before making an appearance. "It took me months and months and months, but I've seen them all now," he confessed.