French President Francois Hollande's former partner, Segolene Royal, has joined the government in a major reshuffle by the ruling Socialists.
She will serve as environment minister in the cabinet of the new Prime Minister, Manuel Valls.
Mr Valls was appointed to the job after the Socialists suffered a humiliating defeat at local elections.
The Finance Minister, Pierre Moscovici, has left the government, with his job now split between two ministers.
It is said that Mr Hollande's most recent official partner, Valerie Trierweiler, had opposed Ms Royal's appointment to any position in the government.
Mr Hollande and Ms Trierweiler officially split up in January amid reports that he had been having an affair with an actress.
The French daily le Monde ran the headline "The revenge of Segolene Royal" on its web edition. One French blogger wrote on Twitter: "Sego [Segolene] nominated, break with Trierweiler complete."
The return of Ms Royal, mother of Mr Hollande's four children, to government follows a long period when she was out of the political spotlight.
She was the Socialist candidate in the 2007 presidential election, but lost to Nicolas Sarkozy.
On Sunday, Mr Sarkozy's centre-right party, the UMP, enjoyed a sweep of French towns, winning previous bastions of the left such as Limoges, Toulouse, Reims and Saint Etienne.
The right-wing Front National had its best ever results, winning control of 11 towns including Beziers and Frejus.
President Hollande is one of the most unpopular French leaders in decades, with his handling of the economy going down particularly badly with voters.
It is open to question how many of the key new appointments were the choice of Mr Valls alone, the BBC's Christian Fraser reports from Paris.
In the new, streamlined government, which has 16 ministers compared with 38 in the previous line-up, Michel Sapin takes charge of finance while Arnaud Montebourg will be in charge of industry and economy.
Mr Sapin is a long-time close friend of Mr Hollande and seen as a safe pair of hands. He was labour minister for the past two years and finance minister in the 1990s.
His first task will be to persuade the EU that France is on track after the country again missed its deficit target, our correspondent says.
The rumour is that Mr Moscovici will be heading to Brussels as the next French commissioner, he adds.
While Mr Valls is on the right of his party, the new Economy Minister, Mr Montebourg, is most definitely to the left, having previously accused the EU of damaging growth with its demands for cuts, our correspondent says.
Mr Valls served in the previous cabinet as interior minister, where he became one of few government figures popular among the wider French public.
His replacement as interior minister is Bernard Cazeneuve, previously the budget minister.
The French have been used to strong characters in the interior ministry, Christian Fraser says.
While Mr Cazeneuve, a lawyer, is an unknown quantity he is certainly not in the strongman image of previous incumbents like Mr Valls or, for that matter, former President Nicolas Sarkozy, our correspondent adds.
Laurent Fabius and Jean-Yves Le Drian keep their positions as foreign affairs and defence ministers in the new cabinet, which replaces that led by Jean-Marc Ayrault.
Two Green ministers from Mr Ayrault's cabinet both resigned in protest at the appointment of Mr Valls as prime minister, because of his tough record on immigration and other issues.
However, the Socialists still enjoy an overall majority in the lower house of the parliament, the National Assembly.
Responding to news of the new cabinet, UMP leader Jean-Francois Cope said he was "very concerned" - adding that the new government would "in no way meet the concerns" of the French.
Front National leader Marine Le Pen dismissed the Valls government as "same faces, same policies and so the same failures".