Keyshawn Johnson had his own real-life Maury Povich moment after a woman claimed he fathered her 4-month-old kid and ... 

KEY ... YOU ARE NOT THE FATHER!!! 

We broke the story, a 35-year-old woman filed court docs claiming Key knocked her up back in 2016 -- right around the time Johnson's wife filed for divorce. The woman wanted child support. 

But Key's attorney Aja Mann tells TMZ Sports the results are in and the test proves Key's not the daddy. 

"Mr. Johnson's only recourse was to submit to the orders of the Court, which included taking a paternity test to dispute these false accusations and the results of course came back negative."

Mann continues, "As he stated before, and states now, Mr. Johnson is not the biological father of this woman's 4 month old child."

"While unfortunate, Mr. Johnson is not the first celebrity to be subjected to false accusations, and he will certainly not be the last."