The king was in the hospital on Thursday due to temporary side effects following his ongoing cancer treatment, according to Buckingham Palace.

Charles' cancer diagnosis was announced in February by Buckingham Palace.

King Charles III was briefly hospitalized Thursday amid ongoing medical treatment for cancer, according to Buckingham Palace.

United Kingdom Prime Minister Keir Starmer presented Trump with a letter from King Charles during a photo op at the White House.

King Charles thanked the medical staff who treated him and his daughter-in-law Kate for cancer this year in his Christmas Day message. He also addressed the summer riots in Britain.

The monarch breaks with tradition in this year’s royal Christmas message, reflecting on a year marked by medical challenges for the royal family.

A royal source tells ABC News that King Charles will be continuing with his treatment into next year and that it is a “managed condition.”

For decades, the two have remained side by side through the ups and downs.

An Indigenous senator and activist shouted "You are not our king" at the British monarch after he finished his speech on Monday. It's Charles' first visit to Australia since he became king in 2022.

Charles is visiting Australia in his first trip to overseas realms since becoming king.

Sen. Lidia Thorpe was escorted out of a parliamentary reception after telling King Charles III that Australia is not his land.

New Zealand's Black Ferns stopped by Buckingham Palace before playing the U.K.'s Red Roses when one of the team's players decided to ask for a royal hug.

King Charles III's coronation will take place at Westminster Abbey on May 6.

The Crown Estate and Duchy of Cornwall Estate released their annual reports.

In a grand ceremony to mark the start of a new Parliament, King Charles delivered a speech, addressing the House of Commons with the laws the new government plans to set.

The English monarch and his daughter-in-law are set to appear at his grand annual birthday ceremony as both deal with cancer treatment.

Activists with Animal Rising said they "redecorated" the painting on Tuesday.

Two of the group's supporters "pasted the face of the iconic British character Wallace over His Majesty’s," the animal rights group said in a press release.

Charles unveiled the portrait himself at Buckingham Palace.

Prince William is now the Colonel-in-Chief of the Army Air Corps.

The monarch made a return to royal duties months after his own cancer diagnosis was revealed.

King Charles is set to resume some public duties this week as he undergoes cancer treatment.

Charles and Queen Camilla will pay a visit to a cancer treatment center on Tuesday, where they plan to meet with patients and staff.

The monarch was sidelined for months undergoing cancer treatment, but his doctors feel confident for him to carry out his royal duties.

Buckingham Palace said that Charles and Queen Camilla will visit a cancer treatment center Tuesday, where they plan to meet with the center's patients and medical staff.

The palace says the king will still undergo cancer treatment and each engagement will be reviewed on a case-by-case basis.

Buckingham Palace announced Charles' cancer diagnosis back in February.

The room off Buckingham Palace's famous balcony will now be accessible to the public.

The monarch made a public appearance to mark the holiday as he undergoes treatment for cancer.

King Charles made his first significant public appearance since announcing his cancer diagnosis in February, celebrating Easter at the St. George’s Chapel in Windsor.

New photos show King Charles III reading some of the thousands of cards he received following his cancer diagnosis.

Buckingham Palace shares new images of King Charles since his cancer diagnosis.

The Duke of Sussex tells ABC News’ Will Reeve he was “grateful” he was able “to get on a plane and go see” his father following the king’s diagnosis.

Harry spoke to "GMA" about his family and the 2025 Invictus Games.

King Charles made his first public appearance since being diagnosed with cancer and he released a statement saying his "most heartfelt thanks for the many messages of support."

Britain's King Charles and Queen Camilla attended a church service this morning near the royals' estate north of London.

King Charles III has made his first public appearance since Buckingham Palace announced he was diagnosed with cancer.

Harry described tensions with his father and brother in his memoir "Spare."

King Charles III became king in 2022. His recent cancer diagnosis has raised questions about what happens in the event of his death or abdication.

As King Charles continues cancer treatment and Princess Kate recovers from abdominal surgery, William is left holding the royal reins.

Both Princess Kate and King Charles III are facing health issues.

Harry, who now lives in California, was seen Tuesday arriving at Clarence House, one day after Buckingham Palace revealed news of the British monarch's cancer battle.

According to Prime Minister Rishi Sunak, the cancer was caught early which was not disclosed when Buckingham Palace made the announcement.

Buckingham Palace shared that the cancer was identified during the 75-year-old monarch’s recent hospital procedure for benign prostate enlargement, but did not specify the type of cancer or treatment.

Buckingham Palace has not provided detailed information about King Charles’ treatment, but other royals have stepped up to help and Prince Harry has returned to the U.K. to see his father.

U.K. Prime Minister Rishi Sunak said Tuesday that King Charles III's cancer was "caught early" and he would "continue to communicate with him as normal."

King Charles III is the oldest child of Queen Elizabeth II, whom he succeeded.

An announcement from Buckingham Palace said, "Subsequent diagnostic tests have identified a form of cancer."

King Charles III, 75, has cancer, Buckingham Palace announced on Monday.

The palace has not specified the type of cancer or type of treatment.