Actress Julie Gayet is suing the magazine that reported she had an affair with French President Francois Hollande.
The move, under France's strict privacy legislation, comes as concern mounts over the well-being of Mr Hollande's partner Valerie Trierweiler, who was hospitalised hours after the magazine published photos of the alleged affair.
The magazine Closer said the 41-year old actress was seeking €50,000 in damages and €4000 in legal costs over the magazine's publication of photos of her and Mr Hollande arriving separately at a borrowed flat near the presidential Elysee Palace.
The president has also said the report was an attack on his right to privacy but has ruled out legal action on his own behalf.
The magazine has promised another series of pictures and fresh revelations about the affair in a new edition on Friday.
Aides to Ms Trierweiler said earlier this week that she had been hospitalised for tests, adding after her stay was extended that she needed further rest. A source close to the couple told AFP that Mr Hollande had not been to visit Ms Trierweiler and confirmed media suggestions that the relationship had been unravelling for months.