French Environment Minister Nicolas Hulot has resigned on live radio, in a dramatic announcement that caught even President Emmanuel Macron by surprise.
The former TV presenter and green activist said he had quit after a series of disappointments in attempts to address climate change and other environmental threats.
Mr Hulot said he felt "all alone" in government.
The decision was taken on the spot and, he added, even his wife did not know.
"I am going to take... the most difficult decision of my life," the minister said in an interview on France Inter radio.
"I am taking the decision to leave the government."
Mr Hulot said that he had not told Mr Macron or Prime Minister Edouard Philippe of his decision, because he believed they would try to talk him out of it.
Mr Hulot is a popular figure in France, and correspondents say his departure is a major blow to Mr Macron, whose ratings are currently poor.
Mr Macron responded to the news by saying he respected Mr Hulot's decision, adding that he hoped to be able to count on his support "in another form".
Government spokesman Benjamin Griveaux said he regretted Mr Hulot's resignation.
"I don't understand why he is stepping down when we had many successes in the first year that are to his credit," he told BFM TV.
The resignation comes a day after the government announced it was relaxing restrictions on hunting. Mr Hulot said that this decision had made him aware of the power of lobbyists.
He also said he was frustrated by the "small steps" being taken to deal with climate change and the fact that "this subject is always relegated to the bottom of the list of priorities".
But the minister said he wanted his resignation to be seen as a wake-up call.
"I hope that my act is not an act of resignation but one of mobilisation," he said.
The well-known presenter of a TV adventure programme, Mr Hulot has campaigned for environmental protection for decades.
Mr Macron was the first president to successfully convince the popular environmentalist to join his government after Mr Hulot turned down previous invitations from Jacques Chirac, Nicolas Sarkozy and François Hollande.