LONDON (AP) — Queen Elizabeth II is poised for another historic milestone, an unprecedented 65 years on the throne.

But Buckingham Palace says Britain's longest-serving monarch plans to spend Monday's ceremonies far from the spotlight in somber contemplation of her late father.

Official commemorations of Elizabeth's Sapphire Jubilee are expected to feature ceremonial cannon fusillades at a central London park and at the riverside Tower of London as well as a procession of military horses pulling World War I-era artillery pieces.

But the 90-year-old monarch is staying 110 miles (175 kilometers) to the north at her Sandringham House estate in Norfolk, where her father, George VI, died of lung cancer at age 56 on Feb. 6, 1952, after a 15-year reign.

Elizabeth surpassed Queen Victoria as Britain's longest-serving monarch in 2015.