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Keira Knightley Image Credit: Rex Features

The life of Diana, Princess of Wales is to be made into a movie — with Keira Knightley tipped to play the lead role.

Producers at film company Pathe have started work on the project and are keen to cast Keira, 25, as Diana — with Dame Helen Mirren, 65, as her mother, Frances Shand Kydd.

Secrecy surrounds the movie, with next year's release date timed to coincide with what would have been the Princess' 50th birthday. The year also marks 30 years since Diana's wedding to Prince Charles. "The project is in the early stages, but Pathe has chosen 2011 quite deliberately," says an insider.

Mirren's success in The Queen — also made by Pathe — has led to the star being earmarked to play Diana's mother. Knightley is at the top of the list of a number of actresses lined up to play Diana. Scarlett Johansson is another possibility.

The film will chart the early years of Diana's life, her ill-fated marriage to Charles, their separation and her death in Paris in 1997.