King Charles III is making a royal move that's never done before: opening the doors to Balmoral Castle.

For the first time since the Aberdeenshire, Scotland, castle was completed in 1855, guests will be granted behind-the-scenes access to the landmark. Queen Elizabeth II, the United Kingdom's longest reigning monarch, died at the private estate at the age of 96 in September 2022; the residence was where the queen and her family would spend summer holidays.

Tickets for the historic event – with tours scheduled between June 1 and Aug. 4 – sold out this week within a day of being released, according to the BBC.

According to its official website, Balmore is the Scottish castle that serves as a beloved home for the royal family, which was purchased for Queen Victoria by Prince Albert in 1852.

Historic opening of royal residences to the public comes amid royals' health battles

The monarch's unprecedented decision to open up royal residences comes amid changes within the monarchy.

The East Wing of Buckingham Palace is set to open to the public for the first time this summer, like Balmoral Castle. Guided tours of the palace's principal floor are scheduled from July through August, per the BBC.

The guided tours also come as seniors members of the royal family are battling health issues. After Catherine, the Princess of Wales, was notably out of the public eye for several months, Kensington Palace shared a video of Princess Kate in which she revealed she had been diagnosed with cancer.

"In January, I underwent major abdominal surgery in London and at the time it was thought that my condition was non-cancerous. The surgery was successful; however, tests after the operation found cancer had been present," Princess Kate said. "My medical team therefore advised that I should undergo a course of preventive chemotherapy and I am now in the early stages of that treatment."

The princess said she was "well and getting stronger every day by focusing on the things that will help me heal in my mind, body and spirits."

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Prior to this revelation, in early February, Buckingham Palace announced King Charles III's cancer diagnosis.

"During The King's recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted. Subsequent diagnostic tests have identified a form of cancer," Buckingham Palace said in a Feb. 5 statement.

Before his diagnosis was revealed, Charles underwent a "corrective procedure" at The London Clinic after the palace had previously announced that the monarch, 75, was seeking treatment for an enlarged prostate.

Contributing: Pamela Avila