Sister Jean Gets Final Four Bling, Big Diamond Ring!!

What do you get a 99-year-old nun as a thank-you present for being the best good luck charm ever??

Diamonds, baby!!!

Loyola-Chicago rewarded Sister Jean -- the superstar team chaplain who was with the Ramblers for every step of their epic NCAA Tournament run last season -- with a Final Four ring Tuesday.

America's favorite nun was courtside for the Loyola's game against Nevada -- when she was handed a dope diamond ring as a present for being the squad's biggest supporter last year.

Sister Jean reportedly had no clue the gift was on its way ... and she smiled huge as team staffers put the band on her hand.

Bad news for Loyola ... they lost the game, 79-65.