She and husband James Matthews welcomed a baby boy into the world Monday at 1:58 p.m. local time, her rep tells E!
Middle child Charlotte was the lightest on his arrival, weighing 8lb 3oz when she was born in May 2015.
An onlooker said hedge fund manager James went home briefly on Monday night to walk the couple's dogs before returning to the hospital.
New Zealand Kiwis stun Australian Kangaroos 26
Some streets around Mt Smart Stadium are lined with Tongan flags and houses decked out in red and white. He hopes that will gradually change, continuing during the looming three-Test series away to England.
We're sure Prince William and Kate Middleton are thrilled Princess Charlotte, Prince George, and Prince Louis will have a new cousin to play with! It took her six weeks after reports started surfacing that she and James were expanding the family for her to confirm it, and even then, she did so covertly in a column about "Exercising During Pregnancy".
"Swimming offers a wonderful feeling of weightlessness", Pippa wrote as she entered her third trimester in the magazine for United Kingdom store Waitrose.
The sisters are said to confide in each other about "everything".
"It's comforting to know that it's safe throughout pregnancy, and you don't need to adapt and change too much".