Barnes councillor Ben Stanberry has resigned.
The Tory councillor was first elected in May 2006.
In his letter of resignation to Richmond's Tory leader, Councillor Nick True, Mr Stanberry said: "On July 1 this year I was appointed as a director of a rapidly expanding medical company and over the last few months it has become a bigger and bigger struggle to fulfil both my obligations as a councillor and as a company director.
"This struggle has also had a significant negative impact on my home life."
He added: "I resign with considerable regret since it has been a huge honour to serve the people of Barnes and of the borough."
The news means the ward will now face a by-election, on December 6.
For more on this story, see this week's Richmond and Twickenham Times.
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