The 44-year-old former supermodel reportedly had a brief but very passionate relationship with Laurent Fabius, 65, before she married the then President Nicolas Sarkozy, in 2008.
Around the this time, political biographer Valerie Benaim wrote a book called Carla and Nicolas: the real story in which she discussed Brunis numerous secret lovers including English rock stars Mick Jagger and Eric Clapton.
One of the most famous Frenchmen whom Bruni dated was former Socialist Prime Minister Fabius. Its true that their relationship was known to the French media, but nobody reported it, the Daily Mail quoted Benaim as saying in an interview four years ago.
The author explained as to why the affair may have been kept secret.
Perhaps because neither Laurent Fabius nor Carla Bruni confirmed their short relationship.
One thing is certain - Carla must like politicians, because she also had an affair with the former minister Luc Ferry, she said.
Ferry, the 61-year-old former education minister, went out with Bruni in the early 2000s, but it is her relationship with Fabius which is now causing a stir in France.
It was brief but very passionate, and its one which we are now going to hear a lot about, a Socialist Party source who knows both former lovers well, said.
At the time Carla was very much a left-winger with plenty of friends in the Socialist Party. Laurent was Frances youngest ever Prime Minister in the mid-1980s, and Carla found this very attractive indeed.
They carried on as a couple in the 2000s, but Mr Fabiuss colleagues and friends were very discreet about the whole thing. Carla herself was very used to conducting secret affairs.
Now people will be very interested in knowing exactly what went on, and everything is likely to be revealed very soon, the source added.
One of Brunis most high-profile affairs was with the philosopher Raphael Enthoven, whom she started sleeping with while officially going out with his father, Jean-Paul Enthoven.
She had a son with Raphael, and was blamed for destroying his marriage to the writer Justine Levy.
But after becoming Frances First Lady she turned into a loyal conservative wife, and had her first child with Sarkozy last year.