The queen has spoken for the first time of how difficult she found it to keep King Charles’s cancer a secret before it was announced publicly.

Camilla found herself “longing to let it out” during an official visit to a Maggie’s cancer support centre in 2024, after Charles had received his diagnosis but before the news was released.

Speaking in a short film, released on the royal family and Maggie’s YouTube channels on Wednesday, to mark the charity’s 30th anniversary, Camilla said she “almost said something” but knew she couldn’t when, as Maggie’s president, she launched its new centre at the Royal Free hospital in London on 31 January 2024.

Maggie’s provides free emotional and practical support to cancer patients and their loved-ones at 27 drop-in centres positioned near NHS hospitals across the UK.

At the time of Camilla’s visit, Charles was recovering from treatment for an enlarged prostate but, as the film reveals, had already been diagnosed with an undisclosed form of cancer, which was eventually announced by Buckingham Palace five days later on 5 February.

“I remember coming to see a Maggie’s just after the king being diagnosed. Nobody could say anything at the time. That was quite difficult,” she told Maggie’s chief executive, Dame Laura Lee, who was filmed in conversation with Camilla at Clarence House.

“I almost said something but, you know, I felt that it wasn’t the time to say.

“[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.”

She told Lee: “I was just longing to let it out but obviously I couldn’t.”

Talking to visitors at the centre during the engagement, she said she was “almost questioning them”, but she did not “want to pry too deeply”.

“But normally when I went in, I was just talking to them, but I don’t know, I felt it was much more deep,” she said.

Charles returned to public-facing engagements in April 2024, less than three months after his treatment began. Speaking of his refusal to slow down, Camilla said: “Look at my husband. Nothing stopped him. He just said, ‘This is my way. I’m going to cope with it.’”

She added: “It had never really come back to roost at home, and suddenly your husband is diagnosed, and you think ‘Goodness I’ve been talking to all these people and now I’m the one with some relation, who’s got to help to look after my poor husband and try and understand it all.’”

Camilla released the seven-minute film to highlight the vital support Maggie’s offers cancer patients, and to promote the services they provide for relatives and especially to men who may be more reluctant to seek help.

She called on every hospital to have a Maggie’s centre. 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.

The organisation offers care for people affected by cancer, including free psychological, emotional and practical support, with no appointments necessary for the drop-in sessions.