Jessica Biel threw a surprise birthday party for boyfriend Justin Timberlake over the weekend.

Approximately one hundred guests, including charttopper Leona Lewis, were invited to celebrate Timberlake’s 28th birthday at The Hollywood Roosevelt Hotel on Sunday.

“Justin was completely blown away when he walked in,” an insider tells E! News.

Party menus includeded buffalo wings, pizza, mini sliders, and homemade cupcakes as guests enjoyed the Super Bowl.

“He thought they were just checking into the hotel and heading to another Super Bowl party. He stopped dead in his tracks when he opened the door and then gave Jessica a kiss.”

“Jessica was in a simple black cotton dress and flats, and worked the room like the perfect hostess,” added the source. “She took breaks to sit with Justin, hold hands and relax.”

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According to reports, the couple is becoming inseparable, and friends of Timberlake have already started claiming that the singer is in “love” with the ‘Home of The Brave’ actress.

Timberlake and Biel were first spotted together at a Golden Globes after-party in January, and were seen getting cozy in Utah during the Sundance Film Festival.

Biel recently took time out to join Timberlake on a Europe tour, where they enjoyed a romantic date at Manchester’s five-star Lowry Hotel.

“Justin’s in love. She’s the coolest chick ever. He wants to be with her all the time. He’s ready to be serious,” People quoted a source, as saying.

The couple were spotted out in Manchester, England, on Saturday holding hands and sharing intimate kisses while on a dinner date at high street restaurant chain Nandos.

They were joined by super-producer Timbaland and Manchester United soccer star Alan Smith.

Timberlake was first linked to The Illusionist actress at the Golden Globes in January (07) – less than a month after he announced his split from girlfriend-of-four-years Cameron Diaz.

A source tells British newspaper The Mirror, “Justin’s really into Jess and when he found out she had some free time he asked her to join him on the U.K.

leg of his tour.

“They’re both doing everything they can to keep their relationship low-profile but when they’re among friends they can hardly keep their hands off each other.”

The couple, who split in January, were spotted enjoying each other’s company at the Whiskey Bar in the Sunset Marquis Hotel on March 9. Later the same weekend, Diaz and Timberlake were reportedly sighted surfing at a Malibu, Calif., beach, according to In Touch magazine.