At the age of 101, British Queen Mother Elizabeth died "peacefully in her sleep" Saturday, Buckingham Palace said. 

She "had become increasingly frail in recent weeks following her bad cough and chest infection over Christmas," a Palace spokesman said. "Her condition deteriorated this morning and her doctors were called." She then passed away.

Her daughter, Queen Elizabeth II, was at her bedside when the matriarch of the royal family died at 3:15 p.m. (10:15 a.m. EST) at Royal Lodge in Windsor, said a Palace spokesman.

Prince Charles, who was very close to his grandmother, and his sons Princes William and Harry were "completely devastated" after being informed of the news on their skiing holiday in Switzerland, a royal spokesman said, and are cutting their holiday short to return home on Sunday. 

Britain's main television and radio channels interrupted regular programs with news of the death, which came during the four day Easter holiday. Expressions of grief and admiration came from national figures and ordinary people from all walks of life.

Her younger daughter, Princess Margaret, died at age 71 less than two months ago. The Queen Mother’s coffin is expected to be moved to the Royal Chapel of All Saints in Windsor Great Park Sunday morning. 

Scores of mourners, some bearing flowers, gathered outside Windsor Castle after hearing the news. They stood at the castle gates, quietly talking among themselves. The bells of the nearby St. John the Baptist church tolled to mark the queen mother's death. 

"She's like everybody's grandmother," said Sheila Livingstone, who left a bunch of flowers at the castle gates. 

Prime Minister Tony Blair said the queen mother was a symbol of Britain's "decency and courage" and the whole nation would join with the royal family in mourning her death. 

"During her long and extraordinary life, her grace, her sense of duty and her remarkable zest for life made her loved and admired by people of all ages and backgrounds, revered within our borders and beyond," he said. 

Former Prime Minister Margaret Thatcher said the queen mother was "a wonderful queen and an extraordinary person." 

"Her death is more than a source of grief to the royal family. It is an irreplaceable loss to the whole nation," she said. 

A brief statement of condolence was issued from the the White House. 

"The president and Mrs. Bush are deeply saddened by the death of the queen mother," said White House spokesman Gordon Johndroe, who was with the president at his Texas ranch. 

She won the country's loyalty and admiration during World War II at the side of King George VI and was as popular at the end of her life as she had been a half-century before, becoming best known to younger generations as the mother of the queen and grandmother of Prince Charles. 

But those of an earlier generation remember her for her loyalty and bravery. They recall when German bombs rained down on London and the country awaited Hitler's invasion, and the queen stayed when she could have fled to Canada, enduring the blitz with them and visiting their shattered homes and bomb shelters. 

As queen consort to the monarch, George VI, she might have been expected to retire from public life at his death in 1952. But after their daughter's succession to the throne, she took a new title, Queen Elizabeth The Queen Mother, and a full load of royal duties, which she carried into her 90s. 

Over two generations of dramatic social change and upheaval, through the abdication crisis that put her reluctant husband on the throne in 1936, the devastation of World War II and the royal family breakups of the 1990s, the Queen Mother emerged as a symbol of the monarchy at its best. 

On her 80th birthday, she even won praise from William Hamilton, a lawmaker who vehemently opposed the monarchy. 

"If there had ever been a revolution in Britain in the last 80 years, she surely would have been spared," Hamilton said. "Unlike some of her brood, she never seems to put a foot wrong." 

The former Lady Elizabeth Bowes Lyon, daughter of a Scottish earl, was married in 1923 to Prince Albert, Duke of York, second son of King George V. 

They had two daughters, Elizabeth and Margaret Rose, and lived quietly until 1936. The duke's elder brother succeeded to the throne that January as King Edward VIII, and by mid-December had abdicated to marry American divorcee Wallis Simpson. 

The Duke of York took the throne as King George VI, a reluctant monarch whom many believed unsuited to the job. 

But the steadfastness and sympathy of the new king and his wife through the deprivation and danger of World War II cemented a bond with the nation that held the Queen Mother firmly in British affections for the next half-century. 

The Queen Mother underwent extensive surgery in 1995 and 1998 for hip replacements, and in 2000, fell and broke her collarbone. Until a few months ago, she continued a regular schedule of public appearances that would have daunted a much younger person. When her health became very frail, she sometimes appeared in public on an electric cart that was christened the "queen mum mobile." 

She helped restore confidence in the throne during unhappiness and scandals in the royal family during the last years of her life, as three of her four grandchildren divorced. The divorce of Princes Charles from Princess Diana and her death in 1997 in a car crash in Paris shook the British monarchy to its core amid widespread anger that the popular princess had been spurned by the royal family. 

While admired for her dignity and sense of duty, the queen mother was also revered for enjoying life. She relished horse racing, social gatherings and was known to enjoy a drink. 

The Associated Press contributed to this report.