Charles, 75, reportedly made personal phone calls to his two sons Prince William and Prince Harry to tell them of his health news before it was announced by Buckingham Palace on Monday.
Harry has since been spotted arriving at LAX and Clarence House on a solo trip to the UK, as he leaves his wife Meghan Markle and their two kids Archie and Lilibet at their Montecito home amid the children's school commitments.
Prince Harry and Meghan have previously used Frogmore Cottage as their UK base, as it is where they lived for six months before stepping back as senior royals and moving their family to America.
The five-bedroom, four-bathroom Grade II listed house located on King Charles' Windsor estate underwent a £2.4 million renovation before the couple moved in with their son Archie, making it the perfect spot for them to stay during their UK visits. However, the Duke and Duchess were asked to hand over the keys in 2023 following the publication of Harry's book Spare.
Sir Michael Stevens, Keeper of the Privy Purse, said: "We can confirm that the Duke and Duchess of Sussex have vacated Frogmore Cottage. The Duke and Duchess have repaid the expenditure incurred by the Sovereign Grant in relation to the renovation of Frogmore Cottage, thus leaving the Crown with a greatly enhanced asset."
In his book, Harry spoke fondly of their former home, stating they were "destined to live" there. "Meg and I moved our office into Buckingham Palace. We also moved into a new home. Frogmore was ready. We loved that place. From the first minute. It felt as if we were destined to live there," he wrote.
"We couldn't wait to wake up in the morning, go for a long walk in the gardens, check in with the swans. Especially grumpy Steve. We met the Queen's gardeners, got to know their names and the names of all the flowers. They were thrilled at how much we appreciated, and praised, their artistry."
When Harry visited London in September 2023 for the annual WellChild awards, there was speculation that he could stay at Windsor Castle while others suggested he ended up in a hotel, even though Frogmore Cottage remained vacant.
He had a 45-minute meeting with his father before Charles was spotted travelling to Buckingham Palace and taking a helicopter to Sandringham in Norfolk. It is not known whether Harry has been granted access to somewhere on the crown estate to maintain his privacy during this sensitive family matter, despite the last-minute arrangements, or if he has chosen alternative hotel accommodation, as per reports.
The Duke has voiced his concerns about his family's security in the past, so we imagine his location will remain under wraps. After royal protection was taken away from Harry and Meghan following their exit from the royal family in 2020, Harry confessed he believes his children cannot "feel at home" in the UK if it is "not possible to keep them safe", he explained in his legal challenge against the Home Office.