It's official: former NDP MP Pierre Nantel is switching teams and running for the Greens in the federal election.

The New Democrats announced Friday that they had removed Nantel as their candidate for Longueuil–Saint-Hubert, following what the party called "confirmed reports" that he was "is in discussions with another party to run under their banner."

On Monday, Green Party Leader Elizabeth May confirmed Nantel will be running as a Green candidate.

"Pierre Nantel is a climate leader, and he is one of the most passionate MPs I have encountered in the House of Commons," said May in a statement.

His switch seems to have come as a shock to his former party.

NDP deputy leader Alexandre Boulerice said he had a short conversation with Nantel last week, during which he talked about the issue of climate change, which is a key part of the NDP's platform.

"It's not a good day for the NDP," Boulerice said Friday. "I don't understand the reasons or the motivations of Pierre."

Nantel was first elected in 2011 as part of the NDP's 'orange wave' in Quebec. He was narrowly re-elected in 2015, beating the Liberal candidate by less than 700 votes.

The NDP said it will now look to nominate a new candidate in the riding.

The Liberals already have recruited a star candidate to run in the riding. Réjean Hébert, a former provincial health minister, announced in July that he would be running for the Liberals.