Britney Spears` engagement ring `cost $90,000`

The singer's fiancé and former manager Jason Trawick got down on one knee on Thursday and presented her with a 3-carat platinum sparkler which she debuted in Las Vegas the following day on Trawick's 40th.

Jewellery expert Michael O'Connor told Us Weekly that Trawick picked the Neil lane design because of the quality of the ring.

'I heard that Jason didn't want a giant stone since he wanted to concentrate on the quality and beauty of a platinum setting,' he said.

'The royal treatment of the ring continues all the way around the finger with platinum set diamonds throughout the entire ring. Only platinum will hold all of that diamond work securely and never fade or change colour over time.'

An insider added that the engagement has been a long time coming for the couple, who have known each other since 2006.

'This is something they've both wanted for a long time,' said the source. 'It's a way to cement their family. They're both extremely happy and can't wait to become man and wife.'