The Duchess of Cambridge's sister's baby was born weighing 8lb and 9oz, with mother and child said to be "doing well".
People confirms the baby boy, who was born on Monday, weighed in at 8 lbs. 9 oz.!
She and husband James Matthews welcomed a baby boy into the world Monday at 1:58 p.m. local time, her rep tells E!
The baby's aunt and uncle Prince William and Kate are "thrilled" at the news, according to a spokesperson for Kensington Palace. Middleton also said that it was important to her to stay fit during her pregnancy.More news: Google+ is officially shutting down
Middleton married financier Matthews past year.
St. Mary's is the same hospital where her older sister, Catherine, Duchess of Cambridge, delivered her children.
In her most recent column, Pippa wrote about the discomfort of her final weeks.
On Friday, Pippa was spotted in public attending the wedding of Princess Eugenie. "That meant I was able to carry on as normal and continue most of my sports with better knowledge and, more importantly, professionals to learn from".
Patients at the highly-respected hospital are given a private room with their own bathroom and satellite TV offering "major global channels".