WASHINGTON (AA) – US President Joe Biden hailed the late Queen Elizabeth II on Thursday, saying the UK’s longest-reigning monarch “defined an era” and was pivotal in deepening relations between the US and UK.

“In a world of constant change, she was a steadying presence and a source of comfort and pride for generations of Britons, including many who have never known their country without her,” the president said in a joint statement with first lady Jill Biden.

“The seven decades of her history-making reign bore witness to an age of unprecedented human advancement and the forward march of human dignity,” he added.

Elizabeth II, 96, was the longest-serving monarch in British history. Buckingham Palace said she “died peacefully” at Balmoral Castle in Scotland.

“The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow,” it added.

The queen had mobility and health issues for the past year stemming from old age. She had to cancel several engagements due to her health and her physician’s advice.

Her final public appearance was during the Platinum Jubilee celebration in June as the monarch marked 70 years on the British throne. A statement issued mid-day Thursday said the queen was placed under “medical supervision” at Balmoral in Aberdeenshire, Scotland.

Biden said the queen “was a stateswoman of unmatched dignity and constancy” whose reign deepened the UK-US alliance as she “helped make our relationship special.”

He said that he looks forward to “continuing a close friendship” with Britain’s new King Charles and his wife, and sent his “deepest condolences to the Royal Family, who are not only mourning their Queen, but their dear mother, grandmother, and great-grandmother.”

“Her legacy will loom large in the pages of British history, and in the story of our world,” he added.

The president ordered all US flags across the country and at American embassies worldwide lowered to half-staff.