Royal sources have claimed King Charles and Prince William are "closer than ever" amid friction with other members of the family.
The King, who was taking part in D-Day commemorative events this week, is said to have dispelled any notion of a rivalry with his elder son.
It comes as both the King and Kate, the Princess of Wales, continue with their respective cancer treatments.
Duties are being spread across the working an increasingly reduced number of royals due to concerns over health issues, the departure of Harry and Meghan from the UK for the US and the withdrawal of Prince Andrew from public life.
According to sources close to the King, he has consulted William on complex family issues involving Prince Andrew and Harry and Meghan. Their joint efforts to tackle these issues are said to have boosted both their personal and working relationship.
A source 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 William added: "He very much wants to support his father. That isn’t something new, but of course, with everything the King is going through with his treatment, he will continue to support him as much as he can."
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It comes after Prince Harry's lawyer said the Duke of Sussex has been given permission to appeal against the rejection of his legal challenge to the British government's decision to take away his police protection when he is in Britain.
The case against the Government is one of several high-profile legal battles Harry has brought in the High Court, with his others involving lawsuits against major players in the British press.
Meanwhile, a Royal insider has claimed King Charles "wants Prince Andrew’s house for Camilla."
According to recent reports, the King isurging his younger brother to vacate the property and move into the smaller Frogmore Cottage that was previously given to Meghan and Harry.
The Duke of York, 64, has the lease on Royal Lodge but Charles controls the purse strings.
A royal source claimed: "The King’s kindness is not without limit and there is a very good option for Andrew to move into Frogmore Cottage, recently vacated by the Duke and Duchess of Sussex, which also has the benefit of being within the Windsor Castle security cordon hence reducing the need for alternative round-the-clock security for Royal Lodge.
"He is taking longer than desirable to recognise the reality of the situation, even though it is clearly the most sensible course of action.
"If he doesn’t agree to move to a property better suited to his needs, then the King may have to reconsider the levels of support he is willing to provide."