PIPPA Middleton is celebrating her engagement to financier boyfriend James Matthews as the smiling bride-to-be showed off her diamond ring after he proposed in the Lake District.

Pictures emerged of the Duchess of Cambridge's younger sister leaving her house with a sparkling diamond on her engagement finger.

Hedge fund boss Mr Matthews got down on bended knee during a trip to the Lake District on Saturday to propose to the Duchess of Cambridge's sister, the Daily Mail said.

The couple have been dating for less than a year, but had moved in together and were last week seen at Wimbledon enjoying the tennis. A delighted Pippa was said to have been totally surprised by the proposal.

On Monday night, Pippa's ring finger was bare when she stepped out at the Frost Summer Party Fundraiser which raises money for the British Heart Foundation's Miles Frost Fund, but on Tuesday morning she was seen wearing the large diamond, surrounded by smaller diamonds.

Pippa leapt into the public consciousness in 2011 when she was her sister's bridesmaid in a figure-hugging Alexander McQueen dress at the royal wedding.

Her nuptials will be one of the most high-profile society weddings since William and Kate married five years ago.

Royal watchers are expecting Prince George and Princess Charlotte to play an important role - as page boy and flower girl, while Kate looks set to be her sister's matron of honour.

Mr Matthews is the elder brother of former Made In Chelsea star Spencer Matthews, who reportedly left the show earlier this year after five series.

The reality television star was also forced to quit I'm A Celebrity ... Get Me Out Of Here! last year because he was taking "steroid-based medication" to bulk up for a charity boxing match.