His character on the hit show was Khal Drogo, a warrior who infamously forced sex on a crying Daenerys Targaryen (played by Emilia Clarke) in the first season.
Momoa has taken Instagram to say sorry for the rape joke, which was reposted on Twitter in the wake of the Harvey Weinstein sexual harassment scandal.
“I am severely disappointed in myself at the insensitivity of my remarks that day,” he says.
“Rape and sexual harassment can reach anyone and I have seen first-hand its painful torment among members of my own family and friends.
“I made a truly tasteless comment. It is unacceptable and I sincerely apologise with a heavy heart for the words I said.”