Nicola also tried to justify her actions, saying she had a "free card" because Tom had really "f***ed up" in the past.
The two briefly split in 2014 after it emerged that he has cheated on her.
The former footballer enjoyed dinner with a group of pals at STK restaurant on Sunday, before getting into a taxi with his camera-shy female companion.
The 36-year-old, who married ex-glamour model Nicola in 2009, didn't have his wedding ring on as he left the upmarket eatery in central London.
Tom tweeted: "Shock – Tom Williams has lunch date with cute blonde", followed by a shocked emoji and an Instagram link.
However, Nicola needn't have been worried, as the "cute blonde" was in fact their son Striker.
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Nicola Mc Lean headed out for date night last weekend, enjoying a dinner out with her husband in London.The star who is rumoured to be re-entering the Big Brother house next year looked casual in her khaki co-ordinates, but had upped the ante with the help of her gold heeled sandals.We think it would look more stylish with a sleek pair of black skinny jeans.While the former Cyprus international star started the meal with a group of friends – sharing a picture of five cocktails on the table – he was seen heading home with an unknown brunette in his taxi.Tom stuck up a middle finger at the paparazzi as he drove off into the night.He went on loan to Peterborough United in March 2001, without having made his senior debut, and the move was made permanent during the summer.