Royal photographer Lord Lichfield has died at the age of 66 after suffering a major stroke.
The Queen was among the first to pay tribute to Lord Lichfield, saying she was "deeply saddened" at the news.
Lord Lichfield was the Queen's first cousin once removed and was the official photographer at the wedding of the Prince of Wales to Diana.
He was being treated in the stroke unit at the John Radcliffe Hospital in Oxford after falling ill.
The renowned photographer had been staying in the area with friends when he suffered a stroke. He died at 0400 GMT on Friday.
A Buckingham Palace spokeswoman said: "It's a private matter. The Queen is deeply saddened and will be sending private condolences."
Lord Lichfield - who inherited the earldom of Lichfield in Staffordshire from his grandfather - has often been asked by the royals to take their official portraits.
He photographed the Queen and the Duke of Edinburgh for her Golden Jubilee in 2002.
In July 1981, he took the official wedding photographs for the Prince of Wales and Lady Diana Spencer.
Tatler editor Geordie Greig said Lord Lichfield was an "old-fashioned gentleman" whose best work had been his shots of the wedding.
"The royal wedding was spectacularly memorable, he got the intimacy of the Royal Family, he got that fairytale magic.
"There was a sort of almost Hollywood magic dust spread throughout that shoot and the world enjoyed it.
"He wasn't complicated, he wasn't pretentious, he wasn't an intellectual, he just loved making beautiful images."
'One of the chaps'
Former royal press secretary Dickie Arbiter said Lord Lichfield had been very close to the Royal Family and was noted for the easy way he handled them during shoots, using a whistle to marshal guests at the wedding of Charles and Diana.
"One year, we were shooting a Christmas card at Windsor Castle it was all over in about 15 minutes, he was almost a one-shot man, he would get it perfect the first time."
Baroness Thatcher, whose recent 80th birthday photos were taken by Lord Lichfield, said: "Patrick Lichfield was not only one of the most talented and professional of photographers, he was also an absolute delight to sit for.
"Always courteous and considerate, he had a rare skill which is now sadly gone."
Friend and photographer Terry O'Neill said Lord Lichfield's style was always spontaneous.
"He did go for the moment. He was instinctive. It was part of his nature."
He remembered that the aristocrat liked to be viewed as "one of the chaps".
In a career spanning 40 years, Lord Lichfield worked for Vogue and photographed many stars, including Sixties singer Marsha Hunt, Michael Caine and Joanna Lumley.
As well as editorial photography, he worked on advertising commissions across several industries, including fashion, tobacco and pharmaceuticals.
He was recently commissioned by the British Tourist Authority, and was involved in Hot Shots, a television series for Discovery Real Time in which amateur photographers are taught by professionals.
Interviewed in October by the BBC News website, he told reporter Caroline Briggs: "Remember that the person you are photographing is 50% of the portrait and you are the other 50%.
"You need the model as much as he or she needs you. If they don't want to help you, it will be a very dull picture."
Lord Lichfield's long-term partner was Lady Annunziata Asquith, and he had had three children with ex-wife Lady Leonora Grosvenor - a son, Tom, and two daughters, Rose and Eloise.