James Gunn's brother Sean "knew from the beginning" that the director was "really cut out" for 'Guardians of the Galaxy'.
The 52-year-old director was recently re-hired by Disney to helm the third instalment in the Marvel trilogy after being fired when a string of controversial old Twitter posts resurfaced and Sean - who plays Kraglin in the Marvel Cinematic Universe films - insisted he always thought the franchise was "exactly the perfect kind of project" for his brother.
Speaking to ComicBook.com, Sean said: "I think I always knew from the beginning that my brother James was really cut out for the job.
"You know like I knew when he was hired that like, wow, this is exactly the perfect kind of project for him.
"So I had high hopes that we would make something good, you know? Then I read the script and I'm like, 'This is fantastic!'
"If we're able to actually make the movie as written on the page, make it pop the way that it does from reading the first script, we're really going to have something here, and I think I was one of the most optimistic people on set from the word go."
As for when he knew the 'Guardians' films were going to be a hit, the 'Gilmore Girls' star admitted that he was "always pretty confident" they "had something massive".
He explained: "I always felt pretty confident that we would have something on our hands, at least that people liked, but I never ever imagined that it would be the massive, massive hit that it was.
"I never thought that they would be able to sell so much. That it would be marketed so well and that kids would identify so well to it and that people would compare it to their favourite 80s movies.
"All of the runaway success was something that I never really expected."