The couple's youngest son, Arthur Chatto, turned 24 on 5 February.
Having previously worked as a personal trainer, as seen in the video below, Arthur joined the Royal Marines after graduating from university. He was pictured wearing his uniform at the late Queen Elizabeth II's Platinum Jubilee celebrations and at her state funeral.
WATCH: The late Queen's great nephew Arthur Chatto opens up about rowing challenge
Arthur used to post regularly on his now-defunct Instagram page, but deleted his account in 2021, after joining the Marines.
Lady Sarah Chatto and Daniel also have an older son, Samuel, 26, and both he and Arthur attended Eton College and the University of Edinburgh.
While they lead fairly private lives, Sam and Arthur have in the past attended public events with the royal family, including Christmas at Sandringham and Prince Harry and Meghan Markle's wedding in 2018.
Sam, who was born in 1996, is Princess Margaret's eldest grandchild. She passed away in 2002 at the age of 71.
Arthur has joined the Royal Marines
Arthur was a page of honour to his great-aunt, the late Queen Elizabeth II, from 2009 to 2015.
The brothers are 28th and 29th in line to the throne respectively behind their mother and their cousins, Charles Armstrong-Jones, Viscount Linley and Lady Margarita Armstrong-Jones.
The Chattos at Queen Elizabeth II's state funeral
Lady Sarah Chatto, tied the knot with the British artist and former actor, Daniel, on 14 July 1994 at St Stephen's, Walbrook, in the City of London.
The late Queen remained close to her niece, Lady Sarah Chatto and her older brother, David Armstrong-Jones throughout her life.
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