In the latest chapter of a legal saga that has helped keep Hollande's complicated private life in the news, lawyers for Patrick Devedjian said the authors of "La Frondeuse" (The Rebel) had defamed their married client.
According to the book, Trierweiler, then a journalist with glossy weekly Paris Match, had, in the early 2000s, conducted simultaneous affairs with Hollande and Devedjian, a minister under former president Nicolas Sarkozy, while still married to her second husband.
Devedjian's advocate, Dan Hazan, said the authors had transformed a salacious rumour into fact purely to boost sales.
"There is not a scrap of evidence that this supposed relationship existed," Hazan said.
Florence Bourg, representing the book's authors, told the court the affair had already been referred to in two previous books and that there was a public interest case for reporting it.
"It sheds light on a political fact of major significance – a sort of non-aggression pact between Hollande and Devedjian at a time when they were both in pursuit of the same woman," Bourg argued.
The book says Devedjian acted as an intermediary between Hollande and then right-wing prime minister Edouard Balladur – a claim the Socialist president described as a fabrication in testimony given to a parallel legal case initiated by Trierweiler.
The unofficial first lady is suing the authors of "La Frondeuse" for defamation and breach of her right to privacy. The Paris court handling both cases is due to rule on Trierweiler's suit on May 27th and on Devedjian's on June 5th.
The book is one of string of publications to have appeared in the last year which focus on the complicated history of her relationship with Hollande and an alleged feud with his former partner Ségolène Royal.
Most of the accounts portray the 48-year-old as a tempestuous personality who keeps Hollande on a tight leash and is ferociously jealous of Royal, the mother of his four children.
Hollande and Trierweiler reportedly became a couple in 2005 but he continued to present himself as Royal's partner until after her unsuccessful presidential campaign in 2007.
Trierweiler's animosity towards her partner's ex became public when she tweeted support for a renegade Socialist who went up against Royal in elections last June and won the parliamentary seat for La Rochelle in western France.