MARY-KATE OLSEN has flipped for a much-older man – and his outraged ex-wife blasts the cradle-robbing romance as “grotesque.”

The 25-year-old former “Full House” star is reportedly in a hot new relationship with Olivier Sarkozy, the 42-year-old New York-based half brother of recently ousted French President Nicolas Sarkozy.

The couple have been dating for about a month and were spotted in the Hamptons, an upper-crust New York suburb, over Memorial Day weekend, according to published reports.

They were quoted as being “head over heels” for one another. But when contacted by The ENQUIRER, Olivier’s ex-wife Charlotte was shocked over her middle-aged ex-husband’s ro­mance with the young actress.

The mom of Olivier’s two teenage children told The ENQUIRER: “That’s not right. It’s grotesque!”

And an insider noted: “Charlotte certainly won’t want her kids to be around Mary-Kate, who has a his­tory of wild-partying and booze binges.”

Adding to Charlotte’s out­rage, the romance comes hot on the heels of stinging reports that linked Olivier to another young woman – 29-year-old actress Stella Schnabel.

Charlotte, a children’s book author, wed investment banker Olivier in 1997 when Mary-Kate was only 10, and in 2010 they became embroiled in a bitter, two-year divorce battle.

Mary-Kate – who with twin sis­ter Ashley is worth $137 million – has never dated anyone as old as Sarkozy. Her prior boyfriend, artist Nate Lowman, was seven years older than she. So was another former boyfriend, the late actor Heath Ledger. But de­spite Charlotte’s objections, the source declared: “Mary-Kate is excited to see where this goes.”