Britain's Queen Mother Elizabeth, 101, known to her loyal subjects as the greatly adored "Queen Mum," died peacefully in her sleep on Saturday afternoon with her daughter, Queen Elizabeth II, 75, at her bedside, representatives for Buckingham Palace said. Her demise, which comes less than two months after the death of her younger daughter, Princess Margaret, who was 71, occurred at 10:15 a.m. ET. "The Queen, with the greatest sadness, has asked for the following announcement to be made immediately. Her beloved mother, Queen Elizabeth, died peacefully in her sleep this afternoon, at Royal Lodge, Windsor," said a statement released by Palace reps. A spokesman for the royal family also told Reuters: "The Queen Mother had become increasingly frail in recent weeks following a bad cough and chest infection over Christmas. Her condition deteriorated this morning, and her doctors were called." The Queen Mother's coffin will be transported to the Royal Chapel of All Saints in Windsor Great Park on Sunday, added the spokesman. A "completely devastated" Prince Charles, who had been on a skiing holiday in Switzerland with his two sons, princes William and Harry, returned to Britain on Sunday, in preparation for the funeral, the Palace reps also stated. The passing of the Queen Mum comes 50 years after the death of her husband, King George VI, whose 1952 passing brought about the ascension of their daughter, Elizabeth, to the throne. However, the deaths of Her Majesty's sister and mother are both somber interruptions to what was to have been her celebratory golden jubilee year.

For more on the Queen Mother's life, read PEOPLE.com's special tribute.