Mr Hollande did not attend the soirée in person, and went on to win the May 6 run-off vote, but Nicolas Sarkozy's camp used the close shave to allege the Socialists had loose morals.
According to campaign staff, Miss Trierweiler, a political journalist who had her own campaign office and this week insisted she had no intention of being a "wallflower", was furious when Mr Dray tried to gatecrash a party reception.
She immediately ordered him out, the sources told Le Parisien, in an incident which will confirm her reputation as a steely operator four days before she and Mr Hollande are due to move into the Elysée Palace. Her name and protective instincts have led some broadcast comedians to call her La Rottweiler.
On Tuesday, she let journalists waiting outside the couple's Paris apartment know who's in charge with a tweet: "I thank my colleagues for respecting our private life and that of our neighbours. Please don't camp in front of our home."
But users of the microblogging site swiftly accused her of being a hypocrite with one writing: "A Paris Match journalist demanding respect for their private life? That's a bit rich!" Miss Trierweiler started dating Mr Hollande in 2005 when his then-partner Miss Royal was beginning to prepare her own presidential candidacy. Mr Hollande and Miss Royal kept a pact of silence about their split, which they only publicly broke after she lost to Mr Sarkozy in 2007.
Miss Royal now wants a top political job, probably as speaker of the lower house of parliament should the Socialists win June legislative elections.
Today she said their four children would not be present for Mr Hollande's presidential inauguration on May 15 at the Elysée Palace, despite the fact that Thomas, their oldest son, had played a major organisational role in his father's campaign.
"We must make an irreproachable republic," she told Canal Plus television.
"François Hollande has been elected president, not his family, not his friends, not his mates.
"My children, moreover, don't wish to be present. They don't think it's their place. There are intimate moments for the family and official moments where protocol must be respected," she said.
She said she would likely attend in her official capacity as president of the Poitou-Charent region and former presidential candidate.
In 2007, Mr Sarkozy invited his whole family, including his second wife Cecilia and his three sons, to a lavish Elysée ceremony, declaring that they would be the Gallic equivalent of the Kennedy's.
Cecilia left him shortly afterwards while Mr Sarkozy was later accused of nepotism for helping his son, Jean, try and become head of the public body running France's biggest business district.