Their romance started on the set of the Wall Street sequel, but there’s no happy ending for Shia LaBeouf, 24, and Carey Mulligan, 25.

"It just wasn’t working," says a friend of the actress, who flew to London after the September split and is now back in L.A., filming the indie Drive.

"She's strong," adds the pal. "She'll be fine!"

As for reports that she has moved on to fellow Brit actor Tom Sturridge, a source tells Us they're just pals: "He dates a British model."