Are Rachel McAdams and Michael Sheen Hollywood's latest bride and groom?

In an exclusive Us Weekly photo, the Morning Glory actress, 32, showed off a brand-new ring on her wedding finger while out and about in L.A. on Sunday. Alas, it's just a ring! A source close to McAdams tells Us she is "100 percent not engaged." Sheen's manager similarly denies the couple of about 10 months are headed for the altar.

The duo became romantic in late summer of last year, and were spotted making out at the Toronto film fest in September. "It may turn serious!" a prescient insider told Us Weekly at the time. They took their romance public in October, holding hands during a stroll in McAdams' native Toronto.

Sheen and ex Kate Beckinsdale have a daughter, Lily, 11. McAdams' on-and-off romance with her The Notebook costar Ryan Gosling -- including a brief engagement -- fizzled for good in 2007.