Here's what would happen if King Charles III stepped down and handed the throne to Prince William

• King Charles III has not indicated that he ever plans to renounce the throne.
• Given his age and historically low popularity in the UK, however, it remains a possibility.

The UK is mourning the loss of a queen that reigned for 70 years while also welcoming a king that spent the same amount of time preparing to replace her.

From the outside, the reign of King Charles III appears to have gotten off to a shockingly good start. In his first speech, he made his intention to follow in his mother's footsteps crystal clear.

"As the Queen herself did with such unswerving devotion, I too now solemnly pledge myself, throughout the remaining time God grants me, to uphold the constitutional principles at the heart of our nation," he said.

Charles, now aged 73, is the oldest person to become king in British history. In the years before Queen Elizabeth II died, speculation mounted that she may have been contemplating stepping down and handing the throne to Charles.

That said, the decades Charles spent as a prince saw his popularity among the public nearly decimated, especially following his divorce from Princess Diana in 1996. As recent as 2021, it led to a desire among the British public for Prince William to succeed Queen Elizabeth II instead of his father, according to a poll on behalf of Newsweek.

Insider spoke to royal experts about what would happen in the event Charles stepped down and what it would mean for the monarchy's future.

Charles couldn't simply step away from the throne

There are two scenarios in which Charles is alive but no longer king, royal historian Marlene Koenig told Insider.

The first comes under the Regency Act, Koenig said, which could be triggered if Charles was physically incapacitated, meaning he could no longer speak or move. Dr. Bob Morris, an honorary senior research associate at UCL's Constitution Unit, told Insider the monarch's inability to carry out their duties would also have to be certified by various people including their spouse.

If that occurred, the next in line – Prince William – would become regent. "He takes over and has all the powers of the king, except some matters, which are reserved," Morris said.

However, there is another, more controversial scenario — abdication. Koenig said it's highly unlikely to ever occur given Charles' intention to follow in his mother's footsteps.

In any case, abdication is a complex process. Charles couldn't simply decide to abdicate by himself. To make it official, he would first need UK Parliament to pass an Act of Abdication, Koenig said.

"He can't just say, 'OK, here it's yours, William.' Nope. The succession to the throne is legislated by parliament," she added.

However, Morris said if Charles really wanted to step back, he could. "The brute fact is if he wanted to go, no one could stop him," Morris said. "But at least the law can provide for the lawful succession of William."

Abdication would shift the entire line of succession forward

One of the consequences of a monarch stepping down is that every other royal in the official line of succession is bumped up a spot, leaving some inheriting more duties, titles, and responsibilities.

If Charles stepped down, William would become king and his son, Prince George, would inherit the Duchy of Cornwall, Koenig said. That inheritance consists of a large portfolio of privately-owned land and assets estimated at as much as $1 billion in March, according to The Guardian.

"If you abdicate, then you have a minor Duke of Cornwall who would be like Prince Charles was in the early years of his mother's reign," she said.

The sudden shift would put pressure on William and his son, Koenig added, who would've been granted a fraction of the time that Charles has had preparing for the top job in the monarchy.

"Why would you put such a burden on William who has not yet had the total expertise? He's only just in the last few years been attending Duchy of Cornwall meetings to learn how to run the Duchy of Cornwall," she said.

The last time a king stepped down, it was seen as a 'dereliction of duty,' Koenig said

Although abdication appears to have become a popular option among other European royal families, such as in Spain and The Netherlands, in the UK it's still regarded as a taboo.

As to why, Morris points to the religious vow of monarchs in places where abdication is somewhat frowned upon. "Our own monarchs have to be members of a particular religion and they feel that they made a religious vow and that they should stick with it," he said.

Koenig said abdication fundamentally does not align with British values. "It's just not in the British nature," she said.

Up until King Edward VIII, the uncle of Queen Elizabeth II, no British monarch in history had ever abdicated voluntarily, Morris added.

When Edward did, Koenig said there was uproar. "To this day, what Edward did to the royal family, it's seen as a dereliction of duty," she added. "It was definitely a constitutional crisis."

But Koenig also said it's important to remember that the UK of the 1930s was a completely different political and social landscape than it is today. "You had Hitler already breathing down your neck. You had the Soviet Union and you also had Oswald Mosley and the British fascists," she said. "It wasn't just a king giving up."

In 1936, she said, abdication was parliament's way of saving the monarchy and ensuring its survival under Queen Elizabeth II.

When it comes to Charles' reign as king, Koenig said abdication would likely only ever be an option in a similar circumstance. "Something would have to happen, it would have to be a huge major scandal," she said.