Fashion designer Mary-Kate Olsen will reportedly marry her fiance Olivier Sarkozy in summer next year.

“They're leaning towards a June event in the Hamptons," usmagazine.com quoted a source as saying.

However, another source suggested that the date might not be final because the duo, who have been engaged for a year now "changed their plans a million times".

“Her family can't even keep up,” the source said.

Mary-Kate, 29, and Sarkozy have been dating since 2012. He reportedly proposed to her with a four-carat vintage Cartier diamond ring purchased for $81,250 at a Sotheby's auction. They were faced marriage rumours this year, but neither confirmed them.

The upcoming nuptials will be Sarkozy's second marriage. He was previously married to Charlotte Bernard and has two children with her.