Kate Middleton's uncle, Gary Goldsmith, admitted to physically assaulting his wife, Julie-Ann Goldsmith, on the 14th of November.
Westminster Magistrates' Court heard that Goldsmith - who is the younger brother of Kate's mother Carole Middleton - left Julie-Ann Goldsmith unconscious outside of their London home.
Gary Goldsmith, 52, attacked Julie-Ann Goldsmith outside their home in Wimpole Street, central London, in the early hours of 13 October.
Prosecutors are seeking a restraining order to ban Mr Goldsmith from contacting his wife, suggesting their marriage is over.
"They both got out of the taxi and [Mr Shepherd] describes Mrs Goldsmith slapping her husband to the face".
Mrs. Goldsmith doesn't remember how it happened, but Gary punched her in the face which knocked her straight to the floor including her head which bounced on the ground.
At the police station, Goldsmith told officers he had pushed his wife hard with his left hand, but denied using a hook.More news: US, ASEAN agree to boost cooperation against terrorism, violent extremism
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Stepping out for the solo royal engagement on the wet and cold day, Kate Middleton opted for knee-high black boots with a slight block heel, which she appeared to wear over black leggings. He was then told to have seen Mr. Goldsmith, the hit violently in the face by pressing a left hook.
Ms Shilton said Goldsmith appeared to be "panicked" and when the taxi driver challenged him over his actions, he became aggressive.
The couple had been at a charity auction at Home House in Portman Square, Marylebone before they clashed.
Goldsmith pleaded guilty to one count of assault by beating. Kate heard specifically how Family Action - one of the charities providing support at the centre - offers perinatal mental health services. What is certain, is that the attorney account to find out how to " protect [Julie-Ann Goldsmith] of this man ".
After he and Luan divorced, he married Julia Leake following a whirlwind romance.
Goldsmith was brought up in a council estate in Hounslow, west London, and had initially worked as an IT operator before becoming an entrepreneur. She met husband Michael at the airline and they later had Kate and Pippa.