Zoey Deutch and Jimmy Tatro are tying the knot ... announcing their engagement on Instagram Sunday -- though it seems this isn't a new development!

The stars shared several sweet snaps in a collab post ... kicking off with one where Zoey's flaunting her ring -- and including a collage of pics from the moment Tatro got down on one knee and popped the question.

It seems Jimmy asked Zoey to marry him at an idyllic beach locale ... and, the two are absolutely beaming in the shots she shared.

Deutch captioned the pics "three months engaged to the love of my life" ... which means this didn't happen just this weekend -- these two lovebirds have been keeping things under wraps for awhile now! Gallery Launch Gallery Getty

Zoey and Jimmy debuted their relationship on Valentine's Day 2

See Full Page