The Duke, one of the richest men in Britain thanks to his vast portfolio of prime property, acquired the prestigious antiques markets in 2005 for a price reported at the time to have been 50 million euros.
The investment has not been a happy one with numerous stall holders having accused the British aristocrat of behaving like a feudal landlord who imposed unrealistic rent hikes on his French 'subjects'.
Bruno Malet, the head of the traders' association in the two markets, bid the Duke good riddance.
"There are currently between 150 and 180 legal actions under way against him, either for refusing to renew leases or for unjustified charges," he said.
"This purchase seems to be very good news. Mr Boutmy seems to be an honest man with good intentions."
The Puces (flea market) of St Ouen consists of 14 markets with a combined total of 1,700 traders. It turns over €400 million a year, three quarters of which is accounted for by antiques dealers.
Jean-Cyrille Boutmy, owner of the Studyrama education and training group, confirmed to AFP that he had acquired the Serpette and Paul-Bert sections of the world famous Saint-Ouen flea market from the Duke's Grosvenor group.
"I bought them last week, in a personal capacity out of passion for the place," he said, declining to confirm a buying price that was put at €25-30 million by financial daily Les Echos.
Asked why he bought the markets Boutmy told Le Parisien: "It's a place full of history and culture and I regularly go there. I fell in love with it right away.
"I want these two markets to hold on to their strength which is their eclectic nature."
Boutmy was not willing to reveal the details of the sale nor the conditions, simply saying it was a "work in progress" that has been going on for a year.
The new owner said his objective was to "reestablish peace" with the traders, in a nod to the unrest caused by the ownership of the Duke of Westminster.