The Mountbatten-Windsor cousins are "remarkably close", according to sources

The royal family has had a difficult start to the year, with both King Charles and the Princess of Wales confirming the news that they have been diagnosed with undisclosed forms of cancer.

The two senior working royals were both forced to take a temporary step back from duty to focus on their respective recoveries, with Prince William having to step up as the heir to the throne. And while King Charles has now returned to duties, Prince William remains to be taking on major responsibilities.

"The weight of the world is on [Prince William's] shoulders," royal expert Robert Jobson explained to HELLO! last month. And as the pressure mounts on the future King, particularly at a time when his wife and father are unwell, his support network is said to be getting tighter.

Inside Prince William's core support network are the Mountbatten-Windsor cousins, particularly Princesses Beatrice and Eugenie, and Peter Phillips and Zara Tindall. 

In fact, the four royals showed their support for Prince William in person this past week, attending a Buckingham Palace garden party on Tuesday, that he was hosting on behalf of King Charles.

"So much has been said about family disunity in recent years that it's sometimes easy to forget how well our senior royals get on with each other," explained royal commentator Rebecca English, via the Daily Mail. "They are remarkably close, in fact."

She continued: "The presence of the younger royals gave Tuesday's event a unique family vibe, as well as an insight into the easy relationship that William enjoys with his cousins. It's a warmth that goes all the way back to fun family summers at Balmoral, Christmases at Sandringham - and now finds expression in the very modern medium of shared family WhatsApp groups."

Prince William is reported to share a particularly close bond with his cousin Peter Phillips, who experts explain is a "sounding board" for the heir to the throne.

"Peter will be a great support to [William] – both as a cousin and as someone who has been there all his life and understands the institution," explained HELLO!'s Royal Editor, Emily Nash. "He has a pragmatic, common sense approach to things and can be a trusted sounding board for the future King.

"Like the rest of the family, I'm sure Peter is lending his support to William and Kate as they face her cancer treatment."

We will continue to update this story.