Pregnancy rumours first emerged earlier this summer, but Emma had kept quiet about the speculation until she posted on her Instagram page on Sunday, August 30 to confirm the happy news.
Showing off her baby bump in a white dress as she grinned broadly alongside "Tron Legacy" star Hedlund, Emma also revealed she's expecting a boy, as she captioned the trio of snaps: "Me...and my two favourite guys."
The post also marks the first time Emma, 29, has shared a picture with Garrett, who she started dating around a year ago, on her social media pages.
Emma, whose father is actor Eric Roberts and aunt is Julia Roberts, was previously engaged to her "American Horror Story" co-star Evan Peters, but they called off their romance for good in early 2019, having dated on and off since 2012.
Meanwhile, Garrett's exes include actress Kirsten Dunst. They ended a four-year romance in 2016.