Mr Devedjian, 68, a married former economic recovery minister in conservative Nicolas Sarkozy’s government, today said he “condemns the author’s claims” that he had an “intimate relationship lasting several years” with Miss Trierweiler, 47, and that she started seeing Mr Hollande, 58, as well when Mr Devedjian refused to leave his wife of 30 years.
Mr Hollande was at the time living with Ségolène Royal, the mother of his four children and a senior Socialist politician in her own right.
There followed a period “a bit like Jules and Jim,” claim the authors of La Frondeuse (The Troublemaker), referring to the 1962 François Truffaut film in which Jeanne Moreau plays Catherine, a woman in a love triangle with her husband and another man, with all three living in the same house.
Miss Trierweiler’s lawyers last night announced she too would file a complaint on the same grounds. Lawyer Frédérique Giffard said: “The nature of the claims in the form of affirmations by the authors alongside unproven, malicious rumours aimed at sullying her and those close to her have led Valérie Trierweiler to take this action.”
Defending the biography, co-author Alix Bouilhaget insisted it was an “honest investigation” whose role was to unravel the “ambiguity that exists between politicians and political journalists”.
At the time of the alleged three-way relationship in the early 2000s, Miss Trierweiler was a political journalist for Paris Match, the weekly glossy magazine, as was her then husband Denis.
The authors claim that at one point during the alleged three-way relationship both Mr Hollande and Mr Devedjian were general secretaries of their respective parties.
“At what moment does one cross the red line? It’s very ambiguous,” said Miss Bouilhaguet, senior reporter at top state channel France 2.
“To have an intimate relationship with the head of the Left or the head of the Right has an impact on political life,” she said.
Miss Trierweiler’s lawyer said that co-author Christophe Jakubyszyn, just named political editor of top French TV channel TF1, “wrongly” claimed to have held several “exclusive interviews” with her for the book.
Mr Jakubyszyn insisted he had met the first lady “several times”, adding that in France today, “for viewer’s information, one is allowed to breach the off the record rule”.
He added: “In the 1980s, people respected the off the record rule and as a result we learned nothing of (former Socialist president) François Mitterrand, state secrets, the court, parallel affairs, illness.”
Mr Mitterrand managed to keep secret the existence of his long-term mistress, ther love child Mazarine and his prostate cancer until shortly before his death.
A spokesman for the Elysee Palace said President Hollande would not be taking legal action over the book.
Justice minister Christiane Taubira was the only cabinet member to offer support to Miss Trierweiler this morning, saying: "She obviously is very exposed, but this is mistreatment."
Interim Socialist party leader Harlem Désir said it was "natural" that she was filing a legal complaint when there is "invasion of privacy or rumours are dressed up as facts."
"I am against reducing public life to gossip columns. We must separate public and private affairs and stop this sort of media exploitation of private persons' lives."