Pippa Middleton and James Matthews have named their son Arthur, according to reports.
Middleton welcomed her first child at the same Lindo Wing of St. Mary's Hospital where her sister and Prince William's children were born.
The inspiration for his other middle name is thought to be from the new mum's brother-in-law Prince William.
The name Michael is a tribute to both Pippa's father and James' younger brother who tragically died while climbing Mount Everest in 1999.
There's also no word on where the name "William" came from, but there doesn't necessarily have to be a familial tie there - it might just be a name that the couple liked... unless he's named after Uncle Prince William, of course.
The Mail On Sunday has reportedly cited the birth certificate for baby Arthur and Pippa's occupation was listed as author on the document.
Michael Middleton and wife Carole.
In 2012, she released her first and only book Celebrate: A Year of British Festivities for Family and Friends.
The newest arrival to the Middleton-Matthews family will also have plenty of cousins to play with. However, the Dugess of Cambridge's younger sister kept the name a secret.
"The Duke and Duchess of Cambridge are thrilled for Pippa and James", Kensington Palace shared in a short statement.
"James and Pippa have had a baby boy", it read.
WATCH: Pregnant Pippa arrives at Princess Eugenie's wedding. "Everyone is delighted and mother and baby are doing well".
Arthur was one of the contenders for Kate Middleton's third child, who was named Prince Louis - with middle names Arthur Charles.