Valerie Trierweiler was hospitalized Friday _ the day the magazine report and photo spread came out _ for "rest and a few tests,'' said her chief of staff, Patrice Biancone. He said she was expected to leave Monday.
Francois Hollande has never married but has had longtime relationships with Trierweiler and before her with French Socialist presidential candidate Segolene Royal, with whom he has four children. Rumors have circulated for months that he might have another lover.
French media face strict privacy laws, but in recent years have chipped away at the tradition of ignoring the private lives of public figures.
The magazine Closer published images Friday showing a bodyguard and a helmeted man it said was Hollande visiting Julie Gayet, 41, a moderately known French actress who appeared in a clip for his 2012 presidential campaign.
Francois Hollande's popularity is already at historic lows over his failure to improve the economy, but a poll released over the weekend indicated the latest developments left the majority of French untroubled.
According to the Ifop poll for the weekly Journal du dimanche, 77 percent of those asked believed the liaison should be private. The poll was released before the hospitalization of Trierweiler was made public.
Francois Hollande himself would agree, saying in a statement that he was weighing possible legal action for "the attacks on respect for privacy, to which each citizen has a right.''
For a president whose approval ratings hover around 25 percent, however, the weekend survey had less good news. More than 8 in 10 said their opinion of him had not changed.
The telephone poll of 1,025 adults was conducted on Friday and Saturday. No margin of error was given in Sunday's publication of its results, but such polls often have one of about 3 percentage points.