Kate Winslet has revealed Dame Helen Mirren broke her own "personal rules" to star in her new Christmas film Goodbye June.

Winslet, 50, made her directorial debut on the drama movie, which was written by her 21-year-old son Joe Anders, which follows four siblings who gather around their dying mother and she takes a turn for the worse over the holiday season.

Mirren, 80, plays the titular mother June and despite initially telling Winslet she never portrays cancer patients of dementia sufferers on screen she broke her own rules after reading the script.

Appearing on The Graham Norton Show, Winslet said: "When I was telling her [Mirren] about the film she said, 'I am going to stop you because I have two personal rules. I will not play anyone with dementia or anyone with cancer.' She still asked to see the script, and then she sent me an email saying she was breaking her own rule because it was such a wonderful project."

Winslet decided she had to step behind the camera to direct - as well as produce and act in Goodbye June - after reading the heartfelt story penned by her son Joe, who father is director Same Mendes.

The Titanic star was touched by the story her son created which was inspired by the death of his own grandmother when he was 13.

She explained: "My wonderful son wrote it. He did a screenwriting course and was encouraged to write from the heart and the most significant thing that had happened to him was the loss of his grandmother when he was 13. When I read it, I said, 'You've written a film and we are going to make it.' I knew I couldn't let it go so now at 50 years old I am a director. It was an extraordinary experience."

Winslet can also be seen in James Cameron's new sci-fi sequel Avatar: Fire and Ash and revealed the director made her fight underwater for her role as Ronal.

She said: "I can't say anything about it, but I do get to hold my breath underwater again and this time I fight underwater too. "It was hard and I never quite mastered it."