Post Malone and Christy Lee have apparently gone from splitsville to proposals ... 'cause the couple is now engaged.

Posty and Christy are seen locking lips in a new video ... but it's the massive rock on her left ring finger that's really got our attention. The diamond is huge!!!

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It's quite the turnaround for the couple.

We broke the story last summer ... Post and Christy had called it quits after dating for several months.

It's unclear when they rekindled their romance, but it looks like Post popped the question on Tuesday in Utah ... with a bunch of friends flying out for the special occasion.

As we reported, Posty started seeing Christy in early 2025, not long after separating from his former fiancée toward the end of 2024.

Nothing says "we're back" like a big ol' diamond.

Congrats!!!