Demi Lovato has signed on to sing the national anthem at the Mayweather vs. McGregor fight on August 26 ... Showtime has confirmed.
Lovato is a HUUUUGE fight fan. She's not only a regular at UFC fights, but also trains MMA at Jay Glazer's gym in Los Angeles.
She also just released her new single "Sorry Not Sorry" last month -- so the timing is great for her.
Also, Diddy and Mark Wahlberg are making a $200k bet on the fight (double or nothing from the Mayweather vs. Pacquiao fight).
Diddy has Floyd.