June 17, 2022 | 1:22pm

Pippa Middleton showed off her growing baby bump while out and about in London on Thursday.

Kate Middleton’s sister, 38, who is already the mother of son Arthur, 3, and daughter Grace, 1, debuted her budding belly at the “Party at the Palace” concert on June 4.

The expectant star wore a green dress to the Platinum Jubilee event, with a source telling Page Six at the time that Pippa is a “natural mama” and “so excited” to expand her family.

The socialite married James Matthews in May 2017. Arthur and Grace arrived in 2018 and 2021, respectively.

While Pippa and the former professional racing driver, 46, keep their little ones’ lives mostly private, the “Celebrate” author has been vocal over the years about staying fit while raising kids.

“Family life and motherhood has consumed much of my spare time and unsurprisingly the challenges I thrived on have taken a back seat,” she explained to Hoka One in a March 2021 interview.

Pippa Middleton
The expectant star debuted her budding belly earlier this month.

“Running and fitness still form part of my weekly routine but not to the level it was before,” Pippa continued.

“I suppose, my running has been more after babies and toddlers than crossing finish lines, which I’m fine with — for now.”

James Matthews and Pippa Middleton
Middleton wed James Matthews in May 2017.
Getty Images

The columnist added that she was intentional about staying “fit and strong” while pregnant for a “mental and emotional reboot,” noting that she now incorporates her kids into her exercise routine.

“Being active with my 2.5-year-old son in the park or playground, transporting him on the back of my bike and buggy running when he was a baby have been ways in which I have been able to include outdoor exercise whilst being a hands-on mummy,” she said at the time.