Justin Timberlake and Jessica Biel will reportedly marry on a private estate later this year.

The couple have been together on-and-off for around five years.

Justin is understood to have popped the question over the Christmas break while the pair were holidaying together.

They have so far kept details of their relationship private, with Jessica only showing off her engagement ring for the first time last weekend.

It's now been suggested they have actually already started planning the nuptials.

"The big day's this summer at a private estate," a source told Us Weekly.

Jessica, 29, is thought to have already decided which designer she will wear on her big day.

The star is apparently a big fan of Monique Lhuillier, who Reese Witherspoon and Jessica Alba also opted for when they got married.

Jessica showed off what appeared to be her engagement ring at a Saturday Night Live celebration in New York City on Saturday.

"It wasn't huge," an onlooker said. "It looked vintage and might have been custom made."