The former 'Bachelor' host announced Monday that he'd popped the question to his entertainment host girlfriend, and she happily accepted, flashing the giant rock and laying a smooch on her hubby-to-be.

Chris took to IG and posted a photo of himself on bended knee and slipping the ring on Lauren's finger, writing ... "I love you @laurenzima The next chapter starts now!" Looks like this engagement moment went down at a winery in Napa Valley.

Lauren -- a host at ET -- reciprocated with her own post, saying ... "We tell each other this all the time, and we said it again in an unforgettably beautiful moment this weekend: I didn’t know love could be like this. You are the most incredible partner. Thank you for loving me, championing me and asking me to marry you. Here’s to the next amazing chapter, and all the rest."

Chris and Lauren have been going strong for at least 2 years now -- they first went public at a pre-SAG Awards party in January 2019, posing on the red carpet together in front of cameras. We've seen them out hand-in-hand several times since then ... even as CH was going through his controversial 'Bachelor' exit. Through it all, Lauren was by his side.

This will be Chris' second marriage -- he was with Gwen Harrison for nearly 18 years, before they split up in 2018. He has two kids from that relationship. This will be Lauren's second marriage as well.