The news of the birth of Pippa and her husband James Matthews' husband came yesterday, with a spokeswoman for the couple reporting that the newborn weighed 8 pounds 9oz.
She added, "Everyone is happy, and mother and baby are fine."
Pippa was taken to the Lindo Wing's private maternity hospital on Monday, which led to rumors that she was in labor.
Husband James was watched as Pippa came to the hospital with a travel bag.
The Lindo Wing was the birthplace of several prominent royals, including the three children of the Duchess of Cambridge, Prince George and Louis and Princess Charlotte.
The Canadian actor Kiefer Sutherland was born in 1
Will Princess Charlotte and Prince George visit Aunt Pippa's new baby today?
While Kate and Pippa's younger brother James was photographed at the Lindo Wing yesterday, the duchess still has to visit her sister.
However, a Kensington Palace spokesman told of her and Prince Willem's joy in giving birth to her nephew.
He said, "The Duke and Duchess of Cambridge are thrilled with Pippa and James."
The children of the Duke and Duchess of Cambridge, Prince George, Princess Charlotte and Prince Louis, will gladly meet their new cousin
It is not yet known if the Cambridge breed is today visit the Lindo Wing to visit Pippas and James's little boy.
The older Cambridge children, George, five, and Charlotte, three, will have had much practice after the arrival of younger brother Louis in April to look after a baby.
Five-month-old Louis was born on April 23, and was not seen in public or royal events except for his baptism on July 9.
The youngest Cambridge was too young to attend the wedding of Princess Eugenie to Jack Brooksbank on October 12, where the older siblings George and Charlotte were pagans and bridesmaids.
George and Charlotte were also pagenboy and bridesmaid for Aunt Pippas's wedding on May 20, 2017.
Pippa married hedge fund manager James Matthews at St. Mark's Church in Berkshire, near Bucklebury Manor – the home of the Middleton family.
James is the elder son and heir of David Matthews, the Laird of Glen Affric.
Should the 43-year-old inherit his father's fatherland, Pippa might become Lady Glen Affric