The 24-year-old Mumford & Sons singer recently popped the question to the 27-year-old actress.
"They're a great couple," a friend of the couple's told Us. "Very sweet."
The pair first met after Carey and pal Jake Gyllenhaal saw Mumford & Sons perform in Nashville, Tenn., on February 7.
"At the end of the night there were just the musicians, Jake, Carey, and the Mumford boys," an insider told the mag at the time. "We had some pizza, and just played music. Jake picked up a guitar and Carey joined in on 'Amazing Grace.' Marcus and Carey seemed really friendly."
Just days after Carey was at Marcus' show in Nashville, the pair reportedly took in an Arcade Fire show together in New York City.
Carey previously dated Shia LaBeouf before splitting in October of 2010. Marcus split with singer Maura Marling in late 2010.
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- Actress Carey Mulligan
- Jake Gyllenhaal
- end of the night
- Arcade Fire