The Queen has spoken publicly for the first time about the "difficult" emotional experience of having to keep the King's cancer diagnosis a secret.
Camilla said she had been "longing to let it out" but that "obviously I couldn't" following her husband's diagnosis, which was officially announced in February 2024.
Speaking as part of a short film made in collaboration with Buckingham Palace to mark the 30th anniversary of the cancer charity Maggie's, the Queen revealed that she "almost said something" but felt the time was not right.
Camilla, who is president of Maggie's, had opened the charity's new cancer support centre at the Royal Free Hospital in London on 31 January 2024, at which time she knew about the King's illness.
The news was announced to the nation five days later.
The Queen said: "Nobody could say anything at the time. That was quite difficult.
"I almost said something, but, you know, I felt that it wasn't the time to say."
Referring to the visit, Maggie's chief executive Dame Laura Lee, who features in the eight-minute film in conversation with Camilla at Clarence House, told the Queen: "It was just a week before it became public and the courage that must have taken for you."
"I was just longing to let it out, but obviously I couldn't," Camilla replied.
"(I) looked at everybody who was suffering and all the relations, and I think it made me realise even more how important these places were."
'Nothing stopped him'
Camilla also spoke about helping to look after her "poor husband", who had also been recovering from treatment for an enlarged prostate, but recalled how he had continued with his work as a way of coping.
"Nothing stopped him. He just said, 'This is my way. I'm going to cope with it.'"
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In December, Charles revealed that his cancer treatment was being reduced, saying in a televised address that the "good news" was "thanks to early diagnosis, effective intervention and adherence to doctors' orders".
Dame Laura said Maggie's had seen a 12% increase in men visiting its centres since the King's diagnosis was announced.
She said: "The King's openness about his diagnosis has undoubtedly helped others to be more open themselves, and to now hear the Queen's completely understandable and natural response as a wife shines a light on why it is so important that family and friends also get the support they need."
Dame Laura also said it was a "huge honour" to hear Camilla speak "so powerfully of her own emotions... while knowing about His Majesty's diagnosis".
Maggie's has 27 centres across the UK, built in the grounds of major NHS cancer hospitals, and supports hundreds of thousands of people each year.
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