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In an interview with the Daily Mirror, Mr Middleton said Catherine and their other sister, Pippa Middleton, have seen him "at my best and at my lowest".

Mr Middleton has credited Catherine, 43, Pippa, 41, and mother Carole, 70, with helping him overcome a mental health crisis in 2017 that lead him to consider taking his own life.

Dame Pippa said the prequel series and film project were being made partly for a "new, younger generation who have also fallen in love with our characters and the challenges they face."

The new, separate film and prequel projects will be written, created and produced by Thomas and executive producers Dame Pippa Harris and Ann Tricklebank, who will also oversee the production of series 16 of the programme together.

Pippa Heylings, the Liberal Democrats' net zero spokesperson, says she thinks part of the pushback is being driven by "big oil and gas" who, she says, have been "emboldened by Donald Trump".