Jacque Seguela, a French advertising mogul who reportedly introduced the couple together in 2007 at a dinner party, revealed the sex of the baby in an interview with a Belgian newspaper, the UK's Telegraph reports.
"I have it on good authority that the baby will [be] a boy," Sequela told Brussels daily Le Soir.
The news comes a week after Sarkozy's father confirmed to a German newspaper that Bruni is expecting. His statement ended weeks of speculation. The French presidential palace has not officially announced Bruni's pregnancy.
On Thursday, the 43-year-old first lady stylishly showed off a distinct baby bump in a white shift dress while hosting a luncheon for the wives attending the G8 Summit in Deauville, France.
At one point, she even gestured towards her belly while posing for photographs.
The baby will be the couple's first child together. Bruni has a 9-year-old son with French philosopher Raphael Enthoven, while Sarkozy, 56, has three sons from two previous marriages.