Prince Philip had reservations about one beloved royal over her hold on King Charles

Prince Philip reportedly had reservations about one of the most popular members of the Royal Family because of the close relationship she shared with his son, Prince Charles, now King Charles.

The late Duke of Edinburgh is said to have had a less than enthusiastic view of the Queen Mother, despite her enormous popularity with the public and members of her own family.

Royal biographer Gyles Brandreth explored Philip's feelings towards his mother-in-law in his book Elizabeth: An Intimate Portrait, drawing on conversations he had with the Duke.

The Queen Mother was widely admired during her lifetime, with her niece Margaret Rhodes telling Brandreth: Everybody adored her. Everybody.

Others described her as captivating and exceptionally charming, but Philip apparently took a rather different view.

When Brandreth asked him about his mother-in-law around the time of her 100th birthday in 2000, Philip offered a notably restrained response.

She certainly keeps going, he told him.

According to Brandreth, Philip's reservations stemmed partly from the treatment he had received from members of the Queen Mother's family when he was courting the future Queen Elizabeth in the 1940s.

But there was another issue that particularly concerned him: the Queen Mother's relationship with Charles.

Brandreth wrote that Philip felt she had an emotional hold over his eldest son that wasn't always to his benefit.

Charles had developed an exceptionally close relationship with his grandmother during his childhood.

Queen Elizabeth became monarch when Charles was only three years old, meaning that his parents were frequently away on official tours during his formative years.

When the Queen travelled overseas, Charles would often remain with the Queen Mother, giving the pair an opportunity to develop a bond that was different from the relationship he had with his parents.

Author Gareth Russell has previously explained that the Queen Mother's role in Charles's childhood was partly a result of the demands placed on Elizabeth after she became Queen.

There were a lot of tours of the Commonwealth and every time the Queen had to go away, Prince Charles stayed with the Queen Mother, Russell said.

He described the pair as having a strong sense of humour and said the Queen Mother always encouraged her grandson.

That close relationship gave Charles a source of support during a childhood in which he had a very different relationship with his father.

Philip was known for having a more reserved personality and reportedly found it difficult at times to connect with his sensitive and artistic eldest son.

The contrast between the two men may have made Charles's bond with his grandmother even more important.

The Queen Mother was warm, outgoing and affectionate, while Philip was considerably more restrained.

Brandreth described Philip as a cool customer and suggested that the Duke found some aspects of his mother-in-law's personality excessive.

Philip's cousin Patricia Mountbatten told Brandreth that he considered the Queen Mother occasionally irritatingly gushing.

Despite his reservations, Philip's comments did not change the fact that the Queen Mother remained an important figure in Charles's life.

For Charles, she had been a source of stability during the early years of his mother's reign and someone with whom he shared a particularly close relationship.

For Philip, however, that same closeness appears to have been a source of concern.