The picture, from 2012, shows Michele and Monteith all cozied up, although the actress didn't share a caption.
This isn't the first time Michele has reminisced about her relationship with Monteith, which began in 2011. In the past, she has posted photos on his birthday, and she recently shared a picture of a tattoo she has of Monteith's "Glee" character Finn's football jersey number.
On the third anniversary of his death last summer, she tweeted:
It's unclear what prompted Michele's most recent throwback photo, but whatever the reason, we love the candid shot.