The announcement was published in the birth announcements section of The Times newspaper. The baby, named Arlo, was born on May 6.
Mr Maclean is an estate agent and longtime friend of the Duke of Cambridge.
He was invited to Prince William’s royal wedding to Kate Middleton in April 2011.
Mr Maclean, who lives in west London, attended Harrow boarding school while Prince William studied at Eton.
He is a qualified chartered surveyor and manages property in the local area and in other places in the UK.
Last week, Kate Middleton’s best friend Emilia Jardine-Paterson also announced the birth of her third child with husband David.
The couple, already parents to sons Leo and Alexander, welcomed daughter Lucia Beatrice India on March 20.
The baby girl’s with was also announced on The Times newspaper.
Emilia (née D’Erlanger) is an interior designer who runs her own company, d’Erlanger and Sloan.
She is one of six-year-old Prince George’s seven godparents.
Ms Jardine-Paterson is a friend of William’s from his teenage years and a school friend of Kate’s from Marlborough College.
She reportedly first introduced the Duke and Duchess of Cambridge.
Her husband David Jardine-Paterson is the scion of a Scottish landowning family descended from the Hong Kong banking Jardines.
Mr David Jardine-Paterson went to Eton at the same time as Prince William.
Like his wife, Mr Jardine-Paterson also has a link to the Middletons: his younger brother, JJ, went out with Pippa Middleton for four years.
Ms Jardine-Paterson is regularly involved in royal circles and was last spotted attending a Sunday service at the Church of St Mary Magdalene on the Sandringham estate in King’s Lynn on January 5, along with the Cambridges and Kate’s parents, Carole and Michael Middleton.
The news comes after the Duchess of Cambridge debuted a new hairstyle on a This Morning appearance.
She was interviewed about her new photography project – the Hold Still 2020.
The Duchess wore her locks down and curled but brushed through.
Some fans took to Twitter to compliment her new style choice.
Twitter user IAmBritish said: “The Duchess of Cambridge looks great with her hair up, don’t you think?”
Another account called Dorset Girly said: “God bless Kate Middleton and her perfect hair.”
Published at Mon, 18 May 2020 06:03:00 +0000