French First Lady Valerie Trierweiler is in hospital in Paris after reports of an affair involving President Francois Hollande and an actress.
Her office said she had been admitted "for rest and some tests".
Mr Hollande's official partner was admitted on Friday, the day Closer magazine revealed the relationship.
Mr Hollande, 59, has not denied secretly visiting actress Julie Gayet at a flat near the Elysee Palace, but has protested at the magazine's invasion of his privacy.
The BBC reports Ms Trierweiler is a journalist for whom he left fellow Socialist politician Segolene Royal, the mother of his four children.
Ms Trierweiler is expected to leave hospital on Monday, her office told AFP news agency.
When asked about the future of her relationship with the president, a spokesperson said she will decide what to do after she has had some rest.