Pippa didn't seem to mind the commotion as she beamed from ear-to-ear and said she "couldn't be happier".
The Duchess of Cambridge's younger sister also flashed her stunning engagement ring – a decadent vintage jewel that featured a halo of diamonds around a central diamond.
Pippa Middleton stepped out in a bridal white summer dress © FameFlynet
Pippa, 32, wore bridal white for her morning appearance. Her Whistles broderie anglaise summer dress showed off her all-year round tan and she completed her chic look with a leather satchel.
Diamond expert David Allen of 77 Diamonds told HELLO!: "Pippa's ring is inspired by the art deco style of the 1920s and 30s. Featuring what looks to be a four carat asscher cut diamond, it is surrounded by an octagonal surround of round brilliant diamonds to give it that feel of yesteryear. Asscher cuts are uniquely clear and require a high clarity, so if this were of top quality, this would fetch in excess of £200,000."
James Matthews proposed with a stunning vintage rock © FameFlynet
A source confirmed to HELLO! that the pretty brunette is to marry her boyfriend James, a hedge fund manager and the older brother of Made in Chelsea star Spencer Matthews.
The happy news comes less than a year after the couple first started dating, with reports stating that James popped the question last weekend during a romantic break in the Lake District.
The engagement, which is said to have taken Pippa by complete surprise, has delighted her family. Her sister Kate and Kate's husband Prince William are said to be thrilled by the news, as are the bride-to-be's parents Carole and Michael Middleton.
Pippa and James first started dating back in 2012. Following their split, she dated banker Nico Jackson for three years but they ended their relationship last year, and in September there were rumours that she had rekindled her romance with James.