Patrick Mahomes' wife, Brittany, really is a bikini model now -- the Sports Illustrated Swimsuit rookie put her stunning body on display during her vacation in Mexico ... and flaunted some serious underboob in the process.
The Kansas City Chiefs superstar and his longtime partner had a romantic trip in Cabo San Lucas over the past several days ... but on Sunday, it was all about the girls.
Brittany was spotted on a luxurious yacht with at least four other ladies ... soaking up the sun as they lounged on the back deck.