Princess Kate's sister is reportedly engaged to her longtime boyfriend James Matthews
Credit: Karwai Tang/WireImage

Is Princess Kate about to take her turn as matron of honor?

Veteran royals reporter Richard Kay broke the news that Kate’s sister Pippa Middleton – who happens to be the world’s most famous bridesmaid – is engaged to her longtime boyfriend, financier James Matthews.

According to Kay, Matthews got down on one knee to propose last weekend while the pair were in the picturesque Lake District of northwest England. (A rep for Middleton has not returned requests for comment.)

Middleton, 32, earlier fueled rumors on Monday when she appeared at a charity fundraiser and notably kept her left hand hidden from photographers.

Attending a gala for the British Heart Foundation, the royal sister-in-law stunned in a floral L.K. Bennett gown alongside Princess Eugenie and Sarah, Duchess of York – but made sure the ring finger of her left hand was never seen.

Middleton and Matthews first dated in 2012 before subsequently splitting – with the party-planning author later dating Nico Jackson for three years.

Three months after Middleton and Jackson parted ways, Matthews, 40, was spotted by Pippa’s side during a St. Barts vacation with her brother, James Middleton.

RELATED VIDEO: 5 Things to Know About Pippa’s Fianc James Matthews!

Middleton and Eton-educated Matthews, who runs Eden Rock Capital Management, have also vacationed together with her family. Last August, Middleton and her family spent time at his parents’ hotel, Eden Rock, in St. Barts.

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Matthews also joined the younger Middletons when they took part in a grueling 47-mile swim-run in Sweden last September.

Most recently, the couple were spotted enjoying Wimbledon together.