There was previously said to be jealousy between Prince William and King Charles, but those close to the family say that is all “a chapter of the past”.

Prince William has become closer than ever to his father King Charles over Prince Harry’s estrangement from the Royal Family, insiders have claimed.

The King is said to see his son as a “useful ally on family matters” following his other son’s departure from life as a senior royal in 2020.

Prince Harry left The Firm with Meghan Markle and subsequently moved to Montecito, California. Since then, he has hardly returned, making special exceptions for the Queen’s funeral, the Invictus Games 10th anniversary, and his legal case.

This strained relationship has only helped to solidify the bond between the King and the Prince of Wales as he puts an increasing amount of trust in his oldest son.

There was previously said to be a “green-eyed monster” between the two as Prince William regularly ranks higher in opinion polls than his father, but those close to the family say that is all “a chapter of the past”.

A friend of King Charles told The Times: “If there was ever a green-eyed monster or a sense of rivalry between the two, that is a chapter of the past. The King sees his son as a useful ally on family matters and increasingly in discharging the duties of nation and state.”

A source close to Prince William also told the publication that he wants to support his father”, particularly during “everything the King is going through with his treatment”.

The rift between Prince Harry and his family has been highlighted recently as the Royal Family attending events marking the 80th anniversary of D-Day while the Duke remained in California.

Experts said this will have prompted Prince Harry to reflect on the extent of the poor relations, particularly with his brother, who took a leading role in the commemorations.

Royal historian and expert Dr Tessa Dunlop has said Prince Harry will have been sad to see Prince William fulfill his duties without him. She told The Mirror: “For the Duke of Sussex, looking on from the other side of the Atlantic, there will be some sadness.

“War is raging in the East of Europe right now and the Duke knows his presence not only captures headlines and boosts the Sussex brand, but helps tie war stories from the past to those in the present day.

“Likewise it is a loss for the Royal Family. The ageing King and Camilla with dutiful William know the drill but lack the pizzazz and lived frontline experience that these events thrive on.”