A source close to the couple tells us the two began a romantic fling recently ... and have gotten pretty serious.

In fact, 26-year-old Genie was just spotted at a fancy restaurant in Pittsburgh this week ... posting a pic of her at the place with the caption, "Pitt stop."

25-year-old Mason -- who was presumably on the other end of the camera -- dropped a "like" on the photo.

Of course, the new relationship means the end of a possible old one for Rudolph ... as we previously reported, the quarterback had been seen in L.A. in April getting cozy with "Bachelor" star Hannah Ann Sluss.

Unclear how serious the two were ... but Rudolph's clearly moved on either way.

As for Genie, she's been no stranger to famous dates in the past ... remember Super Bowl bet guy?!

But, seems she's finally found her special someone ... which is awesome for her, considering just a few months ago she tweeted that going through quarantine "would be a lot more fun with a boyfriend."

Congrats!!