"You can imagine how terrifying it is for a woman to be stuck with a very violent partner, feeling that fear every single day," says Queen Camilla in a forthcoming TV documentary about tackling domestic abuse.

The Queen has been campaigning for many years to raise awareness of domestic and sexual violence - and in this ITV film, she talks candidly to some of its victims.

"By scratching the surface you get a terrible shock. It's such a heinous crime," says the Queen, who has called for domestic violence to be talked about more openly.

The Queen also says in the film that King Charles, who is undergoing cancer treatment, is "doing really well" and that the "problem is trying to stop him".

Queen Camilla has been a longstanding campaigner against domestic abuse and uses this documentary to say it should not be a taboo subject.

"If we could just get more people discussing it..." she says, as she highlights how abuse can mean psychological manipulation as well as physical attacks.

"Coercive control is almost the most frightening bit of domestic abuse. You meet somebody, you think they’re wonderful, attractive, and love you, and then bit by bit they start to undermine you," says Queen Camilla.

"They take away your friends, they take away your family. They take control of your money. They start dressing you. And yet all the time I suppose people still believe they’re doing it because they love them," she says in the documentary, to be screened later this month.

One of the survivors of domestic abuse, who meets the Queen, talks of the "invisible chains" that stop people from escaping, particularly when they have children.

There are also accounts of violence, aggression and threats - and the Queen visits a refuge for women seeking a safe place to escape.

Also appearing is former prime minister Theresa May who talks to human rights lawyer Cherie Blair about changing attitudes to domestic abuse.

"Domestic abuse was something that happened behind closed doors and you didn’t interfere," she says. "Police always used that phrase, 'oh, it’s domestic', and wasn’t anything to do with them.

"Over the years we’ve realised that domestic abuse is wider than what we used to call it... It’s about trying to take control over an individual person's life," adds the former PM.

"Domestic abuse doesn’t have to be physical. And it is actually all about power and control," says Cherie Blair.

The documentary reports that in England and Wales last year more than two million people experienced some form of domestic abuse. On average, every five days a woman was killed by a current or former partner.

In the documentary, the Queen meets Diana Parkes, whose daughter was killed by her estranged husband.

“I think she’s so strong because not many people would be able to survive the death of their daughter. I admire her more than I can say," says the Queen.

The issue of domestic violence has been a consistent theme in the Queen's visits - both in the UK and abroad, including her most recent trip to Australia and Samoa.

At an event at the Commonwealth summit in Samoa, she said there was a "gigantic task ahead of us", needing the support of both men and women. "It is this: to end domestic and sexual violence across the Commonwealth, now and forever."

She had previously warned of a "pandemic" of violence against women and invited campaigners to Buckingham Palace.

In the wake of the murder of Sarah Everard, Camilla said that there was an urgent need to challenge a culture in which it seemed "violence against women is normal".

Her Majesty The Queen: Behind Closed Doors: 11 November, 21.00, ITV1