An inquest will be held to establish the cause of death, but there are no suspicious circumstances and no other parties involved.
Gloucestershire Police said in a statement: “We were called by the ambulance service at 6.25pm on Sunday with a report of the death of a 45-year-old man at an address in the Cotswolds. The death is not being treated as suspicious and a file will be prepared for the coroner.”
Although Lady Gabriella is not a working member of the royal family, she and Mr Kingston’s family are being supported by the Royal Household through this difficult time.
A Buckingham Palace spokesperson said: “The King and the Queen have been informed of Thomas’s death and join Prince and Princess Michael of Kent and all those who knew him in grieving a much-loved member of the family.
“In particular, Their Majesties send their most heartfelt thoughts and prayers to Gabriella and to all the Kingston family.”
In another statement on behalf of Lady Gabriella, Thomas’s parents and his sisters, the Palace said: “It is with the deepest sorrow that we announce the death of Thomas Kingston, our beloved husband, son and brother.
“Tom was an exceptional man who lit up the lives of all who knew him. His death has come as a great shock to the whole family and we ask you to respect our privacy as we mourn his passing.”
Lady Gabriella is the King’s second cousin. They are both great-grandchildren of King George V.
Mr Kingston was a director of Devonport Capital, which specialises in providing finance for companies in “frontier economies”.
The Bristol University graduate had also worked in Baghdad, Iraq, working to procure the release of hostages after joining the Diplomatic Missions Unit of the Foreign Office.
He was a close friend of Pippa Matthews – the Princess of Wales’s sister – and the pair were said to have dated in 2011.
Lady Gabriella, who has worked as an arts and travel director for a brand company, is a writer and contributing editor and also a singer-songwriter.
The couple married at St George’s Chapel, Windsor Castle, in 2019 with Queen Elizabeth II and her husband, the late Duke of Edinburgh, among the guests.
No funeral plans have been released so far.
