Energy and Climate Change Secretary Chris Huhne has confirmed he is separating from his wife and is in a relationship with another woman.
The 55-year-old Liberal Democrat MP for Eastleigh, Hampshire, has been married to Vicky Pryce for 25 years. They have five children and one grandchild.
"I am in a serious relationship with Carina Trimingham and I am separating from my wife," he said in a statement.
Ms Trimingham works in PR. Downing Street did not comment.
A former financial journalist at the Guardian, Independent and the Economist, Mr Huhne made a fortune in the City before entering politics, and is seen as being on the left of the party.
He spent six years as a Euro MP before being elected to the Commons in 2005.
Previously Lib Dem environment spokesman, he ran Nick Clegg close during the 2007 party leadership contest and was later made home affairs spokesman.
Mr Huhne was a key member of the Lib Dem team which held talks about forming the coalition government with the Conservatives.
Ms Trimingham, a former journalist, had been part of his campaign team during the party leadership contest.