EXCLUSIVE

Paris Hilton has yet to return the VERY expensive ring Chris Zylka gave her when he got on bended knee earlier this year, but it may just be a matter of time before she has to fork it over.

Sources close to Chris tell us, he bought the ring -- valued at $2 MILLION. Based on what we know, he got a massive discount. The jeweler and Paris have a close relationship, and publicity for jewelers is as valuable as cold, hard cash.

Now ... we're told Paris is the one who broke off the engagement. Under California law, if she calls off the engagement, he gets the ring back. And, not surprisingly, we're told he wants it back.

We're told Paris and Chris haven't seen each other since the split, and he hasn't requested that she turn the ring back ... but we know he wants it.

It's pretty damn unique, with a massive 20-carat diamond, which took about 4 months to cut.

Play video content 3/28/18 TMZ.com

You'd think something that valuable would've been safe and sound on Paris' finger, but it's been lost and found at least once since Chris proposed in Aspen.