A right-wing politician is to sue the authors of a book on French first lady Valerie Trierweiler that claims she had an affair with him while also seeing the current Socialist president, his office said Thursday.

Patrick Devedjian, who was a minister under ex-president Nicolas Sarkozy, is suing the authors of "La Frondeuse" (The Rebel) for libel and breach of privacy.

The announcement came a day after the first lady herself said, through her lawyer, that she plans to sue the authors of this latest book about her because it spreads malicious rumours.

The work by journalists Christophe Jakubyszyn and Alix Bouilhaguet claims that Trierweiler was having affairs with both Francois Hollande, who was elected president in May, and Devedjian, while she was still married to a third man.

It says that Trierweiler, now 47, was seeing Devedjian in the early 2000s but that Hollande, who at the time was living with Segolene Royal, muscled in when Devedjian refused to commit to her.

Trierweiler's lawyer said the book was based on a collection of "author assertions backed by unproven rumours".

"La Frondeuse" is the latest in a string of works on Trierweiler that have appeared since Hollande was elected, speculating on intense rivalry between Royal and the first lady.

According to the accounts, Hollande first became enamoured of Trierweiler back in the 1980s and they were already a couple in 2007, although he publicly pretended to be still with Royal when she ran unsuccessfully for president that year.