Photo/Illutration Britain's Queen Elizabeth II with Prince Philip in 2011 (AP Photo)

LONDON (AP) — On her 21st birthday in 1947, Princess Elizabeth went on the radio and made a promise to Britain and its Commonwealth nations: She pledged that “my whole life, whether it be short or long, will be devoted to your service.”

Over her very long life, Queen Elizabeth II fulfilled that vow.

Through 15 prime ministers, from Winston Churchill to Liz Truss. Through Britain’s postwar deprivations, crippling labor unrest and Brexit. Through the messy divorces, embarrassments and scandals of her family. She endured through it all — a reassuring anchor in a fast-changing world.

The longest-reigning monarch that Britain has ever known, Elizabeth died Thursday at 96 at Balmoral Castle, her beloved summer home in Scotland, after having steadied and modernized the royal institution through seven decades of huge social change.

Truss pronounced the country “devastated” and called Elizabeth “the rock on which modern Britain was built.”

Her passing ends an era, the modern Elizabethan age. Her 73-year-old son, Charles, automatically became king upon her death. He will be known as King Charles III, although his coronation might not take place for months.

Through countless public events in her 70 years as monarch, Elizabeth likely met more people than anyone in history. Her image — on stamps, coins and bank notes — was among the most reproduced in the world.

But her inner life and opinions remained mostly an enigma. The public saw only glimpses of her personality: her joy watching horse racing at Royal Ascot or being with her beloved Welsh corgi dogs.

Yet Elizabeth had an intuitive bond with many of her subjects that seemed to strengthen over time, keeping a sense of perspective that served her well in most instances, said royal historian Robert Lacey.

“A lot of it comes from her modesty, the fact that she’s very conscious that she’s not important, that she’s there to do a job, that it’s the institution that matters,” he said.

The impact of her loss will be huge and unpredictable, both for the nation and for the monarchy, an institution whose relevance in the 21st century has often been called into question.

World leaders paid tribute to her long reign. U.S. President Joe Biden called her a “stateswoman of unmatched dignity and constancy."

She strongly felt the burden of her role as queen, though she was not destined for the crown from birth.