King Charles: The royals who will step up in his absence

WATCH: King Charles meets with Rishi Sunak Wearing a navy blue suit and tie, King Charles met with Prime Minister Rishi Sunak for the first time since his cancer diagnosis.

LONDON — King Charles is undergoing treatment for a form of cancer, with his son and heir William expected to step up alongside the monarch's siblings and other family members to help carry out public duties during his absence.

Apart from William and his wife Kate, all those who currently carry out royal engagements are aged over 50, with some now in their 80s.

Here are brief details on the Royal Family, the rules of succession and who will step up in the king's absence:

When did Charles become king?

King Charles III succeeded his mother Queen Elizabeth II on the British throne after her death on Sept. 8 2022, becoming king of not just the United Kingdom, but also Australia, Canada, New Zealand and 11 other countries.

Who are the working royals?

Charles had always wanted a slimmed-down Monarchy but after his younger son Harry moved to the United States, and his brother Andrew was forced to step back from public engagements over his ties to the late sex offender Jeffrey Epstein, meaning there are about a dozen active royals.

One of the hardest-working family members is the king's sister Princess Anne, who often tops an annual tally of royal engagements carried out each year.

The king's other younger brother, Prince Edward and his wife Sophie will also be expected to step up and carry out more royal duties to help the king.

Anne, 73, is 17th in line to the British throne while Edward, 59, also known as the Duke of Edinburgh, is 14th.

Kate, Princess of Wales, will not be returning to royal duties until after Easter following abdominal surgery.

What public duties do they have?

Working members of the royal family carry out more than 2,000 official engagements in the U.K. and overseas, which vary from visits to community initiatives, welcoming visiting Heads of State, meeting guests at official Garden Parties and presenting members of the public with honours. They also make foreign visits to strengthen Britain's diplomatic and economic relations.

What are counsellors of state?

As it stands there are no plans to appoint any Counsellors of State to act on behalf of Charles in his absence. Counsellors can be authorized by the monarch to carry out all but the sovereign's most key roles, such as appointing a new prime minister and must be selected from Charles' spouse Queen Camilla, Prince William, Prince Harry, Prince Andrew, Andrew's eldest daughter Princess Beatrice, Princess Anne and Prince Edward.

Who will succeed King Charles?

Under the British constitution, a sovereign succeeds to the throne the moment his or her predecessor dies, before being proclaimed to the people, so there is no interregnum.

The rules, most of which date back hundreds of years, mean the crown passes to the monarch's eldest child, and the line is then dictated by birth order and closeness to the existing sovereign.

So, Charles' eldest son Prince William is the heir to the throne, followed by William's eldest son Prince George, 10, and then his younger children Charlotte, 8, and Louis, 5.

Prince Harry, Charles' younger son and William's brother, is then next in line.

Who are top 10 in line?

Currently the line of succession is:

1) Prince William,

2) Prince George,

3) Princess Charlotte,

4) Prince Louis,

5) Prince Harry,

6) Prince Archie (Harry's son),

7) Princess Lilibet (Harry's daughter),

8) Prince Andrew (Charles' younger brother),

9) Princess Beatrice (Andrew's eldest daughter),

10) Sienna Mapelli Mozzi (Beatrice's daughter).

(Reporting by Michael Holden and Kate Holton; Editing by Angus MacSwan, Alexandra Hudson)