This obscure portrait gave me goosebumps – but I never expected a bidding war | Carol Morley

My film about Audrey Amiss, whose career was overshadowed by illness, was done. Now I had a chance to own a piece of her work

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In late September, I received a direct message on Instagram: Hi, I read a piece you did about the artist Audrey Amiss in the Guardian a few years ago. Wondering if she's still of interest. Think I've found one of her works. Thanks." Sent by Ant Cosgrove of thenorthernartpage, this message arrived just as a BFI-backed feature film I had written and directed, starring Monica Dolan as Amiss and Kelly Macdonald as her psychiatric nurse, was being completed. Conceived at the start of my Wellcome screenwriting fellowship, during which I researched Amiss's vast archive, the title of the film was taken from the occupation she had put in her passport: Typist Artist Pirate King.

I told Cosgrove that I was intrigued" by the possible Amiss work he had found - downplaying the fact that his message had given me goosebumps. He replied that he was a proper art nerd", and outlined how he had researched an unsigned painting coming up for auction. Armed with the title of the piece, Portrait of a Girl, together with the auction house's online photograph of the rear of the frame, on which was written exhibited at the Royal Academy 1957" and Holland Park", he looked into the original catalogue of the exhibition of the Royal Academy of Arts from 1957. While it had no reproductions of the art exhibited, there were three paintings titled Portrait of a Girl - and one of them was by Amiss and gave her address.

Carol Morley is a film-maker, and the director of Typist Artist Pirate King