George Clooney's fiancée Amal Alamuddin flashes her giant engagement ring in London

Amal Alamuddin and her fiancé, George Clooney, toasted to their engagement over the weekend at Bono’s star-studded birthday party.

On Tuesday, however, it was time for Amal to return to work – but not before flashing one very special accessory as she walked through Heathrow airport.

It was hard to miss the human rights barrister’s enormous engagement ring as she ran her fingers through her hair while talking on her phone.

Amal Alamuddin arriving at Heathrow Airport

The exquisite seven-carat diamond, reportedly worth $750,000, is still a fairly new addition to her finger. It was presented to her by fiancé George Clooney on April 22.

Amal looked on top of the world after celebrating the couple’s engagement in Malibu. The pair were toasted by celebrity pals at a bash which also served as a joint birthday party for U2 singer Bono and his 25-year-old daughter Jordan – who share the same 10 May birthday.

The friends also marked George’s birthday – he turned 53 on May 6 – and Randy Gerber’s. George’s business partner celebrated his 52nd year on April 27.

George Clooney’s fiancée showed off her engagement ring

Understandably, the group – which also included Rande’s wife Cindy Crawford and their children Presley and Kaia – were in the mood to party when they arrived at at Cafe Habana, the trendy restaurant owned by Cindy’s husband.

They got stuck in to karaoke, with Cindy singing We Are Family and Bono and Jordan duetting on Something Stupid.

An eyewitness told E! News that the venue was busy with people celebrating Mother’s Day. "They got a show they didn’t expect and other (restaurant patrons) said it was the best Mother’s Day ever."

George proposed to 36-year-old Amal, who is tri-lingual, after seven months of dating.

The future Mr and Mrs Clooney recently returned from a holiday in Cabo, Mexico, where they celebrated a friend’s wedding. "You can tell these two are in love," an onlooker said.

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