Showbiz
Rex Features
The 27-year-old singer reportedly popped the question while the couple were in Italy to attend the wedding of Biel's ex-7th Heaven co-star Beverley Mitchell.
A source told the newspaper: "[Justin] is besotted with Jessica and wants to make an honest woman of her.
"He planned to propose in Rome because it is such a romantic city. Jessica is over the moon and looking forward to a huge wedding. She can't wait."
The source added that Timberlake, who previously dated Britney Spears and Cameron Diaz, has "grown up a lot in the last couple of years and has decided it is time to settle down".
Last month, Timberlake's former 'N Sync bandmate Joey Fatone claimed that the singer had no plans to wed Biel.
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