The Duchess of Cambridge’s sister welcomed her baby boy last month, weighing 8lbs and 9oz, at the Lindo Wing of St Mary's Hospital, Paddington.
According to the Mail on Sunday, the name Michael is believed to be a touching tribute to Middleton’s brother-in-law who died while climbing Mount Everest in 1999.
He is believed to have been on a mission to become the youngest Briton to climb the world’s highest peak
Michael is also the name of Middleton’s father.
Standard Online has contacted representatives of Middleton and Matthews for comment.
The couple brought also their two dogs, a Labrador and a Cocker Spaniel, on the family outing in Chelsea, according to the publication.
At the time, a spokesman for Middleton said: “James and Pippa have had a baby boy.
“He was born Monday 15th October at 1.58pm, weighing 8lb and 9oz. Everyone is delighted and mother and baby are doing well."
The new parents married in May 2017 and announced that they were expecting in June 2018.
The 35-year-old is the younger sister of the Duchess of Cambridge, Kate, who married Prince William in 2011.
She was her elder sister's maid of honour during her wedding.