Mary-Kate Olsen's new boyfriend watch is on - dating Nicolas Sarkozy's Brother Oliver?

Mary-Kate Olsen is reportedly dating Nicolas Sarkozy's brother.

The fashion designer is said to be smitten with Olivier Sarkozy - the younger half-sibling of the former French president - after romancing him for over a month.

According to the New York Post newspaper, the pair are ''head over heels'' for one another and spent Memorial Day weekend together in the exclusive Hamptons resort near New York.

Mary-Kate, 25, previously dated artist Nate Lowman for over two years before splitting in 2010, while 42-year-old Olivier romanced actress Stella Schnabel for a year before their break-up in March.

Olivier was previously married to wife Charlotte and they have two children together.

Last year, Mary-Kate - who shot to fame as a child star alongside twin sister Ashley - was linked to shoe designer Seth Campbell but their romance soon fizzled out.

Before embarking on a relationship with previous boyfriend Nate in 2008, Mary-Kate was linked to a string of men - including the late actor Heath Ledger - but had been officially single since 2005 when she split from Greek shipping heir Stavros Niarchos.

© Bang Showbiz