Pippa was snapped running in the sand and on her phone while sporting shades. She also took a dip in the warm Caribbean waters.
Matthews' family owns the Eden Rock resort in St. Barts.
PIPPA MIDDLETON, KATE MIDDLETON'S YOUNGER SISTER, EXPECTING HER THIRD CHILD
Pippa Middleton looked svelte in a red bikini during a family vacation to St. Barts last weekend. (MEGA)
The Princess of Wales’ sister revealed how she stays fit, telling Hoka in 2021 running has been a "constant" in her life since she was 8 years old.
"Over the past two years, family life and motherhood has consumed much of my spare time and, unsurprisingly, the challenges I thrived on have taken a back seat," Pippa told Hoka. She's been a Hoka brand ambassador since 2018.
Pippa Middleton, who gave birth to her third child less than a year ago, has been an avid runner since she was 8 years old. (MEGA)
"Running and fitness still form part of my weekly routine but not to the level it was before. I suppose my running has been more after babies and toddlers than crossing finish lines, which I’m fine with — for now. Through both pregnancies, I have tried to keep fit and strong for the physical benefits but also for the mental and emotional reboot it gives me."
She said she’s been able to manage her weight by running around the playground, taking her son on the back of her bike and buggy running.
Pippa Middleton carrying Kate Middleton's train at her 2011 wedding with Prince William. (Samir Hussein/WireImage)
Pippa was first thrust into the spotlight in 2011 when she served as older sister Kate’s maid of honor in her Westminster Abbey wedding with Prince William.