Shaun White Says Selena Gomez's Birthday Party Sparked Finneas Bromance

Shaun White and Finneas have Selena Gomez to thank for their bromance ... so says the snowboarding legend himself, who tells TMZ Sports he first met his buddy at the actress/singer's birthday party -- and they've been tight ever since!!

We spoke with White out at LAX this week -- fresh off his snowy adventures on the slopes with Billie Eilish's older bro/music collaborator and their girlfriends -- and he gave us a breakdown of the "Naked" artist's skills following his first time on a snowboard.

"He made turns first day!" White said of Finneas' progress ... joking, "I held his hand a little."

Naturally, we asked how the guys linked up to begin with ... and Shaun admits it was simply bumping into each other at the bar while celebrating Selena's big day (unclear when this interaction went down, but Selena's birthday is July 22).

After that, White invited Finneas to join him for some lessons in the mountains ... and he accepted!!

White says he actually enjoys giving his friends pointers ... 'cause it helps him tune his own skills at the same time!!