Buckingham Palace says Queen Elizabeth II is under medical supervision as doctors are “concerned for Her Majesty’s health.”

The announcement on Thursday comes a day after the 96-year-old monarch canceled a meeting of her Privy Council and was told to rest.

The palace says the queen is “comfortable” and remains at Balmoral Castle in Scotland, where she has spent the summer. The palace declined to provide further details about the seriousness of the queen’s condition.

Here’s everything we know about the queen’s health.

Prince Harry and Meghan, other royal family members going to be with queen

Prince Charles, the heir to the throne, along with his wife, Camilla, and sister, Princess Anne, are already with the queen at Balmoral Castle.

Prince Harry and Duchess Meghan are traveling to Scotland to be by the queen’s side, their spokesperson confirmed to USA TODAY Thursday. A plane landed in the late afternoon local time in Aberdeen, about an hour drive from Balmoral, carrying Prince William, the queen’s sons Prince Andrew and Prince Edward, and Edward’s wife, Sophie, Countess of Wessex, according to the British news company Newsquest, a USA TODAY affiliate.

Doctors have voiced concern for Queen Elizabeth II's health.

Doctors have voiced concern for Queen Elizabeth II’s health.

A look at the British royal family tree,spanning four generations.

Queen Elizabeth II postponed the Privy Council meeting: Doctors advise her to rest

New Prime Minister Liz Truss sends thoughts

Prime Minister Liz Truss said “the whole country will be deeply concerned by the news from Buckingham Palace this lunchtime.”

“My thoughts — and the thoughts of people across our United Kingdom — are with Her Majesty The Queen and her family at this time,” she said on Twitter.

Queen Elizabeth II to skip beloved Highland Games event due to continuing ‘mobility’ issues

Queen’s Privy Council meeting, advised to rest

The latest announcement comes a day after Buckingham Palace revealed Queen Elizabeth II postponed a meeting of senior governmental advisers known as the Privy Council after doctors advised her to rest.

The council had been scheduled to meet virtually on Wednesday, a day after the monarch had a full day of activities as she presided over the ceremonial handover power to the new prime minister at her summer residence in Scotland.

Truss would have taken the oath as First Lord of the Treasury, one of her other titles, and new Cabinet ministers would have been sworn in during the session. The meeting will be rescheduled.

Queen Elizabeth II has had continuing "mobility issues"  over the past year.

Queen Elizabeth II has had continuing “mobility issues” over the past year.

‘It is very nice to be back’: Duchess Meghan, Prince Harry return to UK to promote causes

Queen Elizabeth is going through recent mobility issues

The queen has handed over duties to Prince Charles and other members of the royal family in recent months as she fought to get around.

The queen’s latest postponement comes days after she decided to skip the Braemar Gathering, a popular Highland Games event she loves and attends every year, as she continues to struggle with issues getting around.

Last week, the monarch also decided to formally appoint Britain’s new prime minister on Tuesday at Balmoral Castle rather than make the more than 800-mile round trip to London for the traditional ceremony at Buckingham Palace.

Her eldest son and heir Prince Charles, who normally accompanies the monarch to the Highland Games, will attend in her stead.

Contributing: Amy Haneline, USA TODAY; The Associated Press

This article originally appeared on USA TODAY: Queen Elizabeth health updates: Doctors concerned, Prince Harry visits