The American Horror Story actress, 23, posted a photo of herself and her AHS costar Peters, 28, smooching. In the picture, a casually dressed Roberts plants one on her fiancé, who has a sweater slung over a relaxed outfit of a T-shirt and jeans.
"Happy Birthday to the coolest guy I know," the young star captioned the shot.
Julia Roberts' niece shared the sweet post amidst ongoing rumors of drama between the two costars and lovers. There has long been talk of issues on the set of AHS between Roberts and Peters, but the Palo Alto actress showed with her Instagram that she and her husband-to-be are still very much together.
The Unfabulous alum met the Kick-Ass star while they were filming the comedy Adult World. The performers continued their work together with AHS, in which both stars have held multiple roles.
Peters proposed to Roberts in December 2013, presenting his love with a massive round diamond. The engagement fell just months after an altercation between the two. Police were called to a hotel in Montreal where Peters and Roberts were staying after neighbors overheard a screaming match. Roberts was then arrested, as Peters showed signs of injury.
"They're a couple young kids," a source told Us Weekly at the time. "Their romance is pretty extreme. They just behave in a way that's very passionate."