The Duchess of Cambridge's uncle has admitted hitting his wife in the face and knocking her unconscious after a drunken argument on the way home from a charity event.
"He then describes how Mr Goldsmith punches her hard in the face using a left hook".
Prosecutors are seeking a restraining order to ban Mr Goldsmith from contacting his wife, suggesting their marriage is over.
A taxi driver who took the pair home described how Mrs Goldsmith fell to the floor after he threw a "left hook" at her.
"Both parties are drunk, they had been drinking through..."
The court was told that, when the taxi driver challenged Goldsmith over his actions, he then became aggressive towards him. "He says "She appears to be unconscious, she isn't moving".
After seeing his wife laying on the ground unconscious, Kate Middleton's uncle allegedly began crying and trying to help her get back up.
Goldsmith will be sentenced at the same court on November 21.
At the police station, Goldsmith told officers he had pushed his wife hard with his left hand, but denied using a hook.
The couple had left a charity auction at a private members' club in October when they climbed into a cab and started to fight.
Goldsmith, who appeared in court wearing a blue three-piece suit with a bronze-coloured tie and a patterned handkerchief in his breast pocket, admitted one charge of assault by beating today.
The court heard that he was apologetic for his actions.
It carries a maximum penalty of six months' imprisonment. But I am really looking at how to protect this lady from this man'.
Mr Goldsmith is the younger brother of Carole Middleton and attended the weddings of both her daughters - the Duchess of Cambridge and Pippa Middleton. Shepherd said the couple had got in a row before Julie-Anne slapped her husband across the face.