Tim Robbins Files for Divorce from Gratiela Brancusi

Tim Robbins has filed for divorce, which comes as a surprise ... because we didn't know he was even married.

The "Shawshank Redemption" star filed legal docs Wednesday in L.A. to divorce Gratiela Brancusi ... who he'd been rumored to be dating for about 3 years now.

The 2 were first linked publicly when he brought her to the premiere of his HBO show, "Here and Now," in February 2018, but they attended several more events together in 2019 ... including a family outing at a hockey game in Dec. 2019.

It's unclear when they got hitched ... but he's seeking a dissolution of their marriage now. According to his filing, they don't have any kids together.

As you know ... Robbins was previously with Susan Sarandon. The famous Hollywood couple began dating in the late '80s after meeting on the set of "Bull Durham" and were together for 2 decades, until their split in 2009.