"If you voted for me or #GOTG for the #MTVMovieAwards that's really awesome of you, I appreciate the support. Sadly I will be missing the show," he wrote on his Facebook last Tuesday. "On Sunday I'm joining former Navy SEAL Mike Day as he participates in a grueling half ironman to raise money and awareness for our nations brain injured heroes."
"The Ironman 70.3 or 'Half Ironman' is an endurance race of swimming, biking and running," he further explained. "It's going to be a major challenge and I've trained long and hard for it. ... I hope to help raise awareness and money for a great cause and true hero."
The triathlon was clearly no walk in the park, consisting of a 1.2-mile swim, a 56-mile bike ride and a 13.1-mile run. But Chris completed the course in 7 hours, 4 minutes and 52 seconds.
Check out the video below to see Chris doing more good deeds with his pal Chris Evans, when the two visited Christopher's Haven -- an organization that provides a place for families of children being treated for cancer in nearby Boston hospitals -- after the former Parks and Recreation star lost his Super Bowl bet!