Ryan Seacrest NOT Off the Market ... GF Not Owner of Huge Diamond Ring (PHOTOS)

It looked like Ryan Seacrest was OUT of the dating pool, but the hot chick traveling with him -- with the big ole rock -- is NOT Seacrest's one-time girlfriend.

Ryan hopped a flight in London today with a woman who looks a lot like model Renée Hall -- so much so, the photo agencies identified her as Renée. But TMZ has learned the lucky lady sporting the massive diamond ring is Sarah Mutch. She's reportedly engaged to mega celeb realtor Kurt Rappaport.

Seacrest's reps tell us Ryan was traveling with Kurt and Sarah in Europe.

It's unclear if Renee and Ryan are still a thing -- they haven't been seen together for some time.

So, false alarm -- Ryan NOT engaged, and ... congrats to Sarah and Kurt?

Still, this is as good a reason as any to revisit Renée's hotness.