We knew we would see plenty of surprises at last night's platinum party at the Palace of Buckingham Palace, but this was unexpected!

Kate Middleton's sister, Pippa Middleton Matthews, spotted a noticeable baby bump after appearing at last night's event, and Page Six has confirmed that she is expecting her third child.

Pippa and husband James Matthews, a hedge fund manager and heir to the Lordship of Glen Affric, married in 2017; they are already parents to son Arthur, 3, and daughter Grace, 1.

Kate and Pippa are only two years apart in age, According to Page Six, the two are still "reportedly very close." Pippa rose to international fame as Kate's bridesmaid at her 2011 wedding to Prince William, and since then she has been featured in both 2012's "Celebrate: A Year of Festivities for Families and Friends" (opens in new tab) and 2016's Heartfelt" (opens in new tab).

A source told Page Six that Pippa and her husband James are "very happy" and that Pippa is a "natural mom."

The Matthews family lives at Bucklebury Farm, a 70-acre deer and safari park in West Berkshire that the couple purchased in 2018.

Yesterday was the third day of the ongoing Platinum Jubilee celebrations honoring the 70th anniversary of Her Majesty the Queen's reign. Today is the final day of the celebration, which will conclude with the Platinum Jubilee pageant, attended by Pippa's sister Kate with her three children, Prince George, Princess Charlotte, and Prince Louis. Before attending the pageant this afternoon, the three baked a cake for the big day.