King Charles III has been told he has cancer and has begun treatment in London.

The shocking news comes a week after the 75-year-old British queen left the hospital after another surgery to treat an enlarged prostate.

This is what we know.

How did they find the cancer?

Last month, Charles’ health problems began when Buckingham Palace said on January 17 that the King would go to the hospital for a “corrective procedure” for a benign enlarged prostate.

After showing signs and getting checked out at his home in Birkhall, Aberdeenshire, Scotland, he was given a diagnosis.

After three nights at the private hospital near Regent’s Park, he was released from the London Clinic on January 29 and was said to be “doing well” at the time. He was let go hours after Catherine, Princess of Wales, left the same place where she had been sleeping after a successful surgery on her abdomen.

But while the King was getting that treatment, the palace said on Monday that there was another issue that needed attention. Tests later found “a form of cancer.”

Health experts say it’s not unusual for a lot of people with cancer to be identified while they are getting imaging or medical care for something else.

“You’re going in for one thing, but then you do additional testing — either as part of a general evaluation or influenced by certain symptoms or signs or blood tests that trigger a procedure or imaging — which then leads to the diagnosis of cancer in a different organ system,” said Dr. Anil Rustgi, director of the Herbert Irving Comprehensive Cancer Center at NewYork-Presbyterian/Columbia University Irving Medical Center, who was not involved in Charles’ care.

According to Cleveland Clinic, in most cases, metastatic cancer is not curable. However, treatment can slow growth and ease many of the associated symptoms. It’s possible to live for several years with some types of cancer, even after it has metastasized. Some types of metastatic cancer are potentially curable, including melanoma and colon cancer.

What don’t we know?

The palace has also not said how bad the cancer is or how quickly it was found, nor has it said what kind of treatment the king may be getting. CNN was told by a royal source that it wasn’t prostate cancer, but they didn’t say anything else.

People outside of the royal family rarely talk about their specific medical problems. From the palace’s point of view, they have the right to some medical privacy even though they work for the government. That was the case when the first report of a big prostate came in. But Charles chose to tell others about his diagnosis because he wanted to encourage other guys who might be having symptoms to see a doctor.

When a condition could affect public tasks, things are different. From that point on, the palace had to say what was going on, which is why a statement was made Monday night.

How is King Charles doing?

King Charles was seen for the first time since Sunday, when he got out of the hospital. He seemed happy as he waved to people on their way to St. Mary Magdalene Church in Sandringham, Norfolk, for a Sunday morning service with Queen Camilla by his side.

After that, he went back to London and started outpatient treatment. On Tuesday, he left the city.

The King’s doctors have told him to put off public appearances while he gets treatment. However, he will still be doing state business and official paperwork, the palace said.

He “remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible,” it added.

That means he’ll probably keep getting his daily red boxes of government papers, which he can use to keep going through state papers at home.

The King will likely meet with the prime minister again in person on February 21, according to the UK’s PA news agency.

The meeting between Charles and Prime Minister Rishi Sunak took place over the phone on Wednesday, according to the PA.

CNN has learned that the King will still be able to do official tasks like attend Privy Council meetings. But the specifics of how that will happen are still being worked out.

Tuesday, after his son, Prince Harry, and daughter, Princess Beatrice, paid him a visit, the King went to Sandringham House, the royal family’s private country retreat in Norfolk, eastern England.

The King told Grenada on Wednesday that it had been 50 years since it became independent.