King Charles reportedly advised Prince Harry during a phone call not to bring Meghan Markle to the Queen's deathbed at Balmoral Castle.
His mother and Britain's longest-reigning monarch, Queen Elizabeth II, died on Thursday afternoon (local time) at her estate in Scotland. She was 96.
According to reports, the former Prince of Wales, 73, was alerted via the media to his son and daughter-in-law's initial plan to travel to Scotland as a couple.
Shortly after Buckingham Palace issued a statement regarding the Queen's declining health, a spokesperson for Harry and Meghan - the Duke and Duchess of Sussex - confirmed the couple would be travelling to Scotland together to be with the family.
However, according to the Daily Mail, this announcement "did not go down well" with the royals, who at the time, were reportedly unaware that Harry and Meghan would be paying a visit due to the Queen's deteriorating condition.
"Many behind royal walls, frankly, were incredulous," royal writer Rebecca English claimed.
Mere hours later, Harry, 37, was pictured arriving at the royal residence alone - about an hour and a half after news broke of the Queen's passing.
In the aftermath, a source spoke to The Sun and claimed that Charles had advised his son not to bring Meghan to Balmoral, purportedly calling her presence "inappropriate".
"Charles told Harry that it wasn't right or appropriate for Meghan to be in Balmoral at such a deeply sad time," the source told the tabloid.
"It was pointed out to him that Kate [Middleton] was not going and that the numbers really should be limited to the very closest family. Charles made it very, very clear Meghan would not be welcome."
Kate, now officially Catherine, Princess of Wales, remained at Windsor Castle to care for her three children, while husband Prince William travelled to Balmoral to be with his family. He was photographed arriving at the estate with his uncles Prince Andrew, 62, and Prince Edward, 58, along with his wife Sophie, Countess of Wessex.
Only Charles - now King Charles III - and his sister, Princess Anne, 72, were reportedly by the Queen's side before she passed.
Harry was also spotted leaving Balmoral on Friday to return to England and reunite with Meghan.
The Duke was clearly grief-stricken as he returned to Windsor, with photographs showing him covering his mouth with his hand.
The Sussexes, who have been in Europe for a series of charity events this week, are expected to stay in the UK until the Queen's funeral.
The couple were due to attend the WellChild Awards in London on Thursday, but cancelled when they were alerted to the Queen's declining health.
Prince William made his way back to Windsor on his own. The 40-year-old, who is now officially the Prince of Wales, is the new heir to the throne following the death of the Queen and the ascension of his father.
Meanwhile, Meghan and Harry are understood to be staying at Frogmore Cottage in Windsor.
The Duchess has cancelled a planned appearance on The Tonight Show Starring Jimmy Fallon in New York later this month, and has also postponed the release of the upcoming episode of her Archetypes podcast.
