Boxing’s Floyd Mayweather Jr. was part of a very real tragedy yesterday, according to TMZ Sports.

Their report:

Floyd Mayweather is reeling tonight … because he was on FaceTime with one of his best friends when the guy pulled out a gun, shot his wife and then killed himself … TMZ has learned.

Sources tell us … rapper Earl Hayes called Floyd on FaceTime Monday morning in a rage, over claims his wife — VH1 star Stephanie Moseley — had been unfaithful.

According to our Floyd sources, Earl said he was going to kill his wife. The champ was pleading with him to get a grip … to no avail. Floyd will not say how much he saw, but he acknowledges he was a witness and heard everything.

Floyd is in shock and is having extreme difficulty dealing with the fact that he witnessed a horrifying murder/suicide.