By Kat Giantis
The London Daily Mail says the actress has been swept up in a "whirlwind romance" with Marcus Mumford, the frontman of current "it" band Mumford & Sons, who headlined the basement-set shindig in Tennessee.
"Marcus invited Carey to watch him play a secret show," says a pal. "She sat in the front row, and while he was singing Marcus looked down at Carey and she blushed. It was clear they had chemistry."
Mulligan, who's currently calling New York home, is apparently "besotted" with the London-based musician and has enjoyed a couple recent getaways with him in their native Britain.
"Carey's hoping they can spend more time together when Marcus flies back to America next month for a major tour with his band," continues the snitch. "He's hired a vintage train instead of a tour bus and has asked Carey to join him for the trip. It's early days, but they seem to enjoy each other's company."
Carey called it quits with Shia LaBeouf last October after a year of coupledom. In recent months, she's been briefly linked to fellow British thespians Tom Sturridge and Eddie Redmayne.
Mumford previously dated singer-songwriter Laura Marling. For those not up on your indie love triangles, Marling had been involved with Charlie Fink of Noah and the Whale. After their breakup, Fink chronicled his heartbreak on the band's 2009 album "The First Days of Spring."
Wonderwall.com goes behind the scenes at the 2015 American Music AwardsWatch Video »
In honor of the 10th anniversary of "Just Friends," check out how the stars of the film have changed.Watch Video »
Get the Duggar dish on Replay hosted by Wonderwall's Kirby Kristen.Watch Video »
Tats for Love
From Heidi Klum and Seal to Ryan Sweeting and Kaley Cuoco, see which stars got tattoos for love.Watch Video »
Shailene Woodley and the stars of "Divergent" chat phobias and on-set injuries at the film's world premiere.Watch Video »
Stars chat with Wonderwall.com on the red carpet at the 2015 American Music AwardsWatch Video »