Prince George, Queen Elizabeth
Prince George grabs the attention of his grandmother, Queen Elizabeth II, outside Princess Charlotte’s christening in England on July 5, 2015. Reuters

Amid growing concerns over Queen Elizabeth II's health, rumors about her death as well as her abdication have made the rounds. The 90-year-old monarch was forced to skip annual royal holiday celebrations, including Christmas and New Year services, due to a "heavy cold."

The world's longest serving monarch's illness has given rise to questions about which British monarch would become the first king to sit on the throne since 1952. The queen has four children — Prince Charles, Princess Anne, Prince Andrew and Prince Edward. Prince Charles, the eldest, is the first in line to be king. But his wife Camilla, the Duchess of Cornwall, is unlikely to become the next queen of England due to her troubled past over her relationship with Charles while he was still married to the late Princess Diana.

The line of succession is based on the first-born and then his or her children. If the first-born does not have any children, the crown will pass on to the next-eldest sibling. So, if Prince Charles didn't have any children, next in line after him would be Princess Anne. But since he has two sons, Prince William, the elder brother, will be next in line after Charles. If William were to die, his son Prince George would be next in line to the throne.

If William were to take the throne, his wife Kate Middleton, the Duchess of Cambridge, is likely to hold the ceremonial title of queen without having any claim to the throne.

Queen Elizabeth II took the throne in 1952 after King George VI's death, who didn't have any sons. At the time, the law favored sons over daughters. But in 2011, the Act of Settlement was changed before Prince George’s birth to ensure succession would not be affected by gender of the child.

The fourth in line to the throne is William and Middleton's daughter Princess Charlotte. She can become England’s queen after her elder brother dies or abdicates before fathering an heir or if something happens to his heirs.

Currently, William’s brother Prince Harry is fifth in line to the throne, following George and Charlotte. This could change in the near future if William and Middleton decide to have more children.