The Princess of Wales was allegedly concerned for her mother, Carole Middleton, after she and Prince William informed her parents about their engagement, which coincided closely with the death of a close family member.

Royal author Robert Jobson reveals that William sought Michael Middleton's blessing for his daughter's hand in marriage at Birkhall, on the Queen's Balmoral Estate, on October 30.

However, they postponed the announcement of their engagement due to the passing of Catherine's paternal grandfather, Peter, on November 2.

As a result of this unfortunate timing and the delay in sharing the news, Jobson suggests that Catherine was anxious that Carole might not have been informed about the proposal.

He wrote: "On 30 October, William invited Kate's parents to Birkhall on the Queen's Balmoral Estate. It was there that the prince - knowing his bride-to-be had accepted his proposal - asked Michael Middleton for his daughter's hand in marriage.

"They were preparing to announce the news on 3 November, once he had told the rest of his family, but the death on the day before of Catherine's ninety year old paternal grandfather, Peter, at this home in Hampshire, caused them to delay.

"Catherine explained that the confusion meant she did not even know if her mother, Carole, knew about the proposal," reports .

Carole Middleton's 70th birthday this week has sparked a flurry of best wishes across the UK, including heartfelt messages from King Charles and top-ranking Royals who are reportedly quite taken with Princess Kate's mother.

As covered by the Daily Express, insiders suggest that she's held in high esteem by the Royal Family.

Commenting on Carole's rapport with the royals, the monarch's ex-butler, Grant Harrold, hinted that a bash might have been on the cards for the mother of the future queen consort. He speculated: "As it's a special birthday, I definitely think the King and Queen will be doing some sort of party for her, maybe in London as they like to mark special occasions.

"And they will usually buy Carole a birthday gift but for her 70th it will be something more special as Carole plays an important role in the Royal Family. For the party there will be lots of members of the Royal Family invited as well as the Middletons and obviously William and Kate. But they may also throw her their own party or dinner."

While details of such an event remain under wraps, Carole's son James Middleton paid tribute to his mum on Instagram by writing: "Happy 70th Birthday to my darling Mother. My Hero."

Kensington Palace refused to comment.