Julia Roberts seldom posts on social media but couldn't resist sharing a film still of herself in character in Gaslit, which aired its latest episode on Sunday night.MORE: Julia Roberts shares rare selfie as she makes exciting announcementThe Pretty Woman star plays Martha Mitchell in the series, which is a modern take on the 1970s political Watergate scandal.Julia stars alongside Sean Penn, who plays John Mitchell, and did not look happy in her chosen film still, which was accompanied with the caption: "The Mitchells are not getting along. Gaslit tonight on Starz."VIDEO: Julia Roberts' love story with husband Danny Moder revealed Julia plays Martha, a socialite from Arkansas who becomes the first person to publicly speak about Nixon’s involvement in the Watergate break in.MORE: Julia Roberts' incredible property portfolio revealedRELATED: Julia Roberts' unique living situation with husband Danny Moder and their three kidsSean plays her husband, an Attorney General.