Puff Daddy -- Confirms Biggie Banged Anthony Mason's GF

Sean "Puff Daddy" Combs is backing up Fat Joe's claim that Notorious B.I.G. banged Anthony Mason's GF ... saying the mystery Knick in "I Got A Story To Tell" is in fact Mason ... 100%.

Combs called into "The Breakfast Club" when Charlamagne asked if the bombshell revelation Fat Joe made on ESPN's "Highly Questionable" was factual ... or hip-hop fable?

Fat Joe tapped Mason as the NY Knick in the classic rap song -- in which Biggie rhymes about banging a guy's GF ... then robbing him when the BF walked in on it (tough night).

Puff spilled the last bit of the beans ... saying he "could confirm that story with love" ... admitting B.I.G. did the same thing to Mason's GF that Michael Jordan did to the Knicks for the entire '90s.