• Pippa Middleton and husband James Matthews are expecting their third baby, a report says
  • Kate Middleton's sister was spotted with a noticeable baby bump at the "Party at the Palace" concert in London Saturday
  • Pippa joined her older sister, brother-in-law Prince William and other royals at the star-studded event 

Kate Middleton may have a new family member on the way.

Pippa Middleton, the younger sister of the Duchess of Cambridge, is pregnant with her third child with husband James Matthews, Page Six reported. International Business Times could not independently verify the information.

The 38-year-old author was spotted at the star-studded "Party at the Palace" concert in London Saturday with a noticeable baby bump, according to the outlet. The concert was part of the ongoing festivities for Queen Elizabeth's Platinum Jubilee, celebrating her 70-year reign.

The couple is "so happy" over the pregnancy, and Pippa is a "natural mama," an unnamed insider told Page Six. They are already parents to son Arthur Michael, 3, and daughter Grace Elizabeth, 1.

Pippa is close to Duchess Kate and served as a bridesmaid when her older sister married Prince William in 2011.

Back in 2017, an unnamed Middleton family friend told Us Weekly that it was a longtime dream for the two sisters to be pregnant at the same time.

At the time, Prince William and Duchess Kate only had two children — Prince George and Princess Charlotte. But the royal couple welcomed their youngest child Prince Louis in 2018, the same year Pippa and Matthews welcomed their son Arthur.

Pippa tied the knot with the hedge fund manager and heir to the lairdship of Glen Affric in May 2017. A year later, the couple purchased Bucklebury Farm, a 70-acre deer and safari park in West Berkshire, England.

In honor of Queen Elizabeth's Platinum Jubilee, the farm has been hosting family events spanning four days in celebration of the monarch's 70 years on the throne.

Pippa joined her sister and brother-in-law at Saturday's "Party at the Palace" concert, along with other members of the royal family, including Prince Charles, Prince George, Princess Charlotte, Princess Anne and Prince Edward.

The Queen did not attend the concert due to her ongoing mobility issues, People reported.

Meghan Markle and Prince Harry also did not join the festivities. The couple is spending the day privately as a family to celebrate their daughter Lilibet's first birthday. They also share 3-year-old son Archie.

The concert featured performances by Queen, Elton John, Alicia Keys, Hans Zimmer, Duran Duran, Andrea Bocelli and Diana Ross.

Andrew Lloyd Webber and Lin-Manuel Miranda also appeared in a special performance featuring casts and special guests from "The Phantom of The Opera," "Hamilton," "Six," "The Lion King" and "Joseph and The Amazing Technicolor Dreamcoat."

The Platinum Jubilee celebrations will culminate Sunday with the Platinum Jubilee Pageant.

Pippa Middleton, Kate Middleton
Pippa Middleton may not choose Kate Middleton as her son's godmother. Pictured: Middleton sisters react while watching the action from the Royal Box of the men's singles final match between Britain's Andy Murray and Switzerland's Roger Federer on Centre Court on day 13 of the 2012 Wimbledon Championships tennis tournament at the All England Tennis Club in Wimbledon, southwest London, on July 8, 2012. Getty Images/Leon Neal/AFP