Mary-Kate Olsen. (AP Files)

Mary-Kate Olsen has shot down reports she's set to wed her artist boyfriend Nate Lowman.

The former child star, 23, was rumoured to have accepted Lowman's proposal of marriage during a romantic break in Paris, France, earlier this month, and made plans for a wedding next year.

A source revealed to America's Star magazine that the actress' beau had popped the question after a candlelit meal, hiding the ring in a box of chocolates.

The pal said, "At the end of the meal, Nate gave her a truffle box. But inside, she found a little jewellery box instead. When she opened it, there was a beautiful engagement ring.

"Mary-Kate was absolutely swept off her feet by Nate's proposal. She's so thrilled, she can barely keep it quiet."

Other reports suggested the pair was battling over plans for a pre-nuptial agreement to protect Olsen's millions.

An insider told the National Enquirer, "Their love has grown to the point where it's time to take the next step in their relationship. Because many millions of dollars are at stake, there's no question that Mary-Kate's legal advisers will make sure a pre-nup is ironed out, and Nate's signature is on the dotted line."

But Olsen's spokesperson insists the young star has no plans to head to the altar with Lowman, 30.

Her representative says, "There's absolutely no truth to any of this."

Olsen has been dating Lowman since last year.