eric williams & jennifer williams*Hmmm, looks like there’s been some hanky panky going on right under now ex “Basket Ball Wife” Jennifer Williams’ nose and she was clueless.

Williams’ estranged husband, former NBA player Eric Williams, allegedly had a secret child in 2011 … and now the baby mama wants him to pony up some child support ASAP.

Tavia Serena Cannon filed a Complaint for Support in PA last week, she claims she had a child with Eric in October 2011. Cannon says she makes $300/week babysitting and wants Williams to fork over some cash and medical coverage for the kid.

Here’s the rub … at the time the baby was allegedly conceived — Jan/Feb 2011 — the former NBAer was still married to Jennifer … who didn’t file for divorce until June 2011.

Sources close to Jennifer tell TMZ this news comes as a shock. They claim the “BB Wife” had NO CLUE about the child. Their divorce is still pending in a NJ court.

Calls to Eric Williamss rep have not been returned.