NFL's Mason Rudolph Goes IG Official With Genie Bouchard, 'My Valentine'

It's official -- Mason Rudolph and tennis star Genie Bouchard are an item ... and we know this, 'cause the NFL QB made the announcement Sunday with a steamy IG pic of the two in Cabo!

As we previously reported, Bouchard and Rudolph began dating in the fall ... but the two had carefully avoided any public appearances or social media shoutouts.

That all changed Sunday, though ... when 25-year-old Rudolph posted a smokin'-hot flick of the couple in swimsuits on a beach in Mexico.

"My valentine," Rudolph captioned the photo, adding a heart emoji.

Interestingly, 26-year-old Bouchard did NOT post Rudolph ... though she did confirm her Cabo vacay was a "quick vday getaway."

A few of Rudolph's Steelers teammates congratulated the quarterback on the relationship ... with Eric Ebron, Zach Banner and Terrell Edmunds all showing love.

Of course, Bouchard and Rudolph are no strangers to high-profile relationships ... Rudolph was just spotted last year with "Bachelor" star Hannah Ann, while Bouchard famously went on a date with a guy after losing a Super Bowl bet.