Lebron James -- Marries High School Sweetheart Savannah Brinson

Lebron James tied the knot in California last night -- and instead of some crappy band "We Are Family" -- playing at the reception ... they got JAY Z and BEYONCE!!!!

The Miami Heat forward and his fiancee Savannah Brinson made things official during a ceremony in San Diego at the Grand Del Mar Hotel ... after dating 12 years.

According to reports -- the 28-year-old basketball player was joined by teammate Dwyane Wade and his girlfriend Gabrielle Union ... Chris Bosh and wife Adrienne ... as well as Jay Z and Beyonce, who performed "Crazy in Love" at the reception.

... and you thought the picture booth at your wedding was cool.