12:59 PM PT -- 1/13 -- Brandy is denying all involvement, with a rep for the singer telling TMZ ... "Brandy never saw the ring and has no knowledge of it ever being in her presence. It was never a part of her look for the event."
9:01 AM PT -- A rep for Ashley Thomas tells TMZ they deny the allegations and that he "looks forward to presenting the facts in the appropriate forum."
Brandy Norwood is being dragged to court over a $45,000 ring she was supposed to wear at the American Music Awards ... a ring that's allegedly gone missing.
Brandy and her stylist, Ashley Sean Thomas, are being sued by Elle B. Mambetov, a fashion designer and Beverly Hills store owner.
In the lawsuit, obtained by TMZ, Mambetov claims Brandy's stylist approached her last year about borrowing jewelry and clothes for the singer to wear at the November Awards show ... and the designer let them borrow some outfits and a Dreamboule Big Bang Diamond Ring.
Brandy and her stylist allegedly never returned the ring ... and the designer claims it's valued at around $45k. She says in her suit Brandy's stylist told her it was last seen on the piano at Brandy's Calabasas estate.
Brandy didn't wear the ring or the outfit to the AMAs ... but we're told it's not all that uncommon, because stylists usually put together many different options for celebs.
The ring is 18-karat rose gold, with a sapphire crystal dome and black volcanic stone.