BFM Television said the Elysee presidential palace had confirmed that Trierweiler had been hospitalised since Friday because of exhaustion. French daily Le Parisien said earlier on its website that Trierweiler, shaken by the revelations about the affair, had been taken to hospital on Thursday, right after hearing about Hollande's liaison.
The paper said doctors had prescribed rest and that she would be discharged in a few days. Trierweiler's spokesperson was not immediately available. On Friday, Hollande threatened to sue celebrity magazine Closer, complaining of breach of privacy after it said he was having an affair with actress Julie Gayet.
Hollande and Trierweiler, a journalist for celebrity magazine Paris Match, are not married but have been in a long-term relationship for several years.
French first lady in hospital to "rest", says spokesman
French first lady Valerie Trierweiler's spokesman confirmed on Sunday that she had been admitted to hospital in Paris needing "rest", but said would be discharged on Monday.
"She has been in hospital since Friday. She will leave tomorrow," her spokesman Patrice Biancone told Reuters.
The daily newspaper Le Parisien said earlier on Sunday that Trierweiler had been taken to hospital after being shaken by reports of an affair between her partner, French President Francois Hollande, and an actress.
Asked about the future of Trierweiler's relationship with the president, Biancone said: "She needs rest. Then she will decide what to do."