Many fans already know that former "The Office" star John Krasinski screen tested for the role of Captain America, and that Chris Evans was ultimately cast. Last night on "Conan," however, the actor revealed when he knew the part wasn't for him after "Thor" star Chris Hemsworth's muscles ended up scaring him away.

Krasinski, who recently gained 25 pounds of muscle for his role in director Michael Bay's "13 Hours: The Secret Soldiers of Benghazi," got to wear the Captain America suit on set, a great experience for a huge Marvel fan like him. The actor said that while he felt "pretty good" about his musculature while testing for the film, he had a change of heart.

"All of a sudden Chris Hemsworth walked by as Thor and was like 'Hey mate!' and I'm like... 'I'm good. This is stupid. It's okay. I'm not Captain America. It's fine,'" he said.

You can watch the entire "Conan" clip below:

While he didn't suit up in the Marvel Cinematic Universe, Krasinski has still been quite busy, starring in and directing "The Hollars," which opens this weekend, and will return to TV as Jack Ryan in Amazon's upcoming "Jack Ryan" TV adaptation. He also executive produced the upcoming drama "Manchester by the Sea" and serves in the same role on Spike TV's "Lip Sync Battle."

"Captain America: The First Avenger," starring Evans in the titular role, as well as Hayley Atwell, Sebastian Stan and Dominic Cooper, was released on July 22, 2011. It has spawned two sequels, "Captain America: The Winter Soldier" and "Captain America: Civil War," and the character has also appeared in a number of other Marvel films.