Bill Belichick is secretly the Bill Belichick of music -- so says his longtime girlfriend who just revealed the Patriots coach is a closet SINGING SENSATION!
Linda Holliday dropped the musical bombshell in an interview with N Magazine, saying:
"I’ll tell you something about Bill ... He can sing. And he can sing well."
She noted, "You won’t hear it. You won’t see it. But he can sing well.”
Belichick -- who was sitting next to Holliday for the interview -- reportedly busted out a "boyish grin" when Linda spilled his secret.