"The Boy is Mine," an R&B-pop novella and vocal tit for tat about a man both were dating, earned both women their first No. 1 crossover hit and (surprisingly) the only Grammy award for either, for best R&B performance by a duo or group.

Brandy and Monica appeared on the Wednesday, June 25, edition of 'The Tonight Show with Jimmy Fallon' during which they revealed the surprising inspiration behind their hit duet 'The Boy Is Mine.'