Rumours of her relationship with James emerged last September when the couple were spotted enjoying a late-night dog walk together shortly after Pippa split up with boyfriend of three years, Nico Jackson.
The following morning Miss Middleton was photographed outside his apartment holding a bouquet of flowers.
Pippa holds Kate's bridal gown at her wedding (Pascal Le Segretain/Getty Images)
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The pair have been inseparable ever since and, although neither has officially confirmed their relationship, Miss Middleton's car has been spotted outside Mr Matthew's apartment on numerous occasions.
The Middleton's are said to be pleased with the news
Adam Pretty/Getty Images
A friend of the couple told the Daily Mail: "I can confirm that Pippa and James are engaged. They are saying nothing more at this stage."
Another friend said that James and Pippa were drawn together through their mutual love of outdoor activities, saying: "They love physical challenges. Pippa has swum the Bosphorus, climbed Mont Blanc and cycled across America.
Pippa hid her ring from photographers at the Frost Summer Paty last night
Ian West/PA
"It makes them a good match. Earlier this year they completed 33 mile cross country ski race in Norway."
They added: "Many people will say what a lucky guy James is for landing Pippa. I would say she’s the lucky one. He’s one hell of a catch."
Pictured a charity fundraiser yesterday evening Miss Middleton - who published cookbook 'Celebrate' in 2012 - hid her left hand as she posed for photographs.
