Royal photographer Lord Lichfield remains seriously ill in hospital after suffering a stroke.
Lord Lichfield is in Oxford's John Radcliffe Hospital
Lord Lichfield, 66, is the Queen's first cousin once removed and was the official photographer at the wedding of the Prince of Wales to Diana.
A spokesman for the John Radcliffe Hospital in Oxford said he was "very, very poorly".
The renowned photographer was admitted to the Stroke Unit after becoming ill while staying with friends.
Lichfield Studios said the earl, 66, had family members with him and was waiting for test results.
"He has been diagnosed as having had a stroke and is currently admitted to the Stroke Unit," it said on Thursday.
Lord Lichfield, one of the UK's best-known photographers, has often been asked by the royals to take their official portraits.
He photographed the Queen and the Duke of Edinburgh for couple's Golden Jubilee in 2002.
In July 1981, he took the official wedding photographs for the Prince of Wales and Lady Diana Spencer.
In a career spanning 40 years, Lord Lichfield has worked for Vogue and photographed many stars, including Sixties singer Marsha Hunt, Michael Caine and Joanna Lumley.
Patrick Lichfield first picked up a camera at the age of six and took his first pictures of the Queen as he one day played cricket against Eton.
He was a soldier in the Grenadier Guards before becoming an assistant in a photographic studio in London.
In the early 1960s he struck out on his own and worked for newspapers and magazines, including Life. He also was given a five-year contract with American Vogue.
As well as editorial photography, he worked on advertising commissions across several industries, including fashion, tobacco and pharmaceuticals.
Recently the British Tourist Authority commissioned Lord Lichfield and each year he shoots the Unipart Calendar in locations around the world.
He has been awarded fellowships of both the British Institute of Professional Photographers and the Royal Photographic Society.
He has recently been involved in Hot Shots, a television series for Discovery Real Time, where 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."