Ryan Reynolds and Blake Lively

Happy birthday to Ryan Reynolds!

The actor, who turned 35 on Sunday, is celebrating this weekend with someone special: Blake Lively.

The Green Lantern costars – and their dogs – were spotted Saturday morning outside an apartment in Boston, where he's filming the action film, R.I.P.D.

And this is no casual birthday meet-up. "They are very much a couple," a source tells WHO. "They're really happy together."

Lively, 24, recently split from Leonardo DiCaprio after a summer romance, and Reynolds is still friendly with his ex, Scarlett Johansson.