Jennifer Lopez is clapping back at Jose Canseco -- shutting down his public accusations that Alex Rodriguez cheated on her with Canseco's ex-wife, Jessica.
J Lo appeared on "The Breakfast Club" on Wednesday where Charlamagne Tha God asked about Canseco's tweets where he called out A-Rod and then challenged him to a fight.
"I mean, it doesn't matter," Lopez said ... "I know what the truth is. I know who [Alex] is. He knows who I am.