Film giants 20th Century Fox are behind the adaptation of Cathy MacPhail's Inverclyde-set book Another Me.
Acclaimed director Isabel Coixet was a fan of the novel and developed a screen play, recruiting top actors including Jonathan Rhys Meyers and Rhys Ifans to play the characters.
Now the first phase of filming for the psychological thriller, called Panda Eyes, has been completed in Cardiff and is set to move to Spanish city Barcelona in the New Year. Award-winning writer Cathy, who is involved in the film as an executive producer, said she is overjoyed with it and can't wait for it to be released.
She told the Telegraph: "I am absolutely delighted. This is a massive achievement."
The main character is played by actress Sophie Turner who stars in American drama Game of Thrones and the film also stars Gregg Sulkin and Clara Forlani, who starred in Meet Joe Black alongside Brad Pitt.
Cathy, who has met the stars and travelled to Cardiff to watch filming, said: "Another Me started out as a short story and became a novel. It is a creepy tale about a girl who is haunted by her doppelganger.
"The novel is set in Greenock, as are most of my books, and the steps which run from Dempster Street to Prospecthill Street play a big part.
"I used to walk to school and work on these steps and in the book they are thick with fog, which adds to the atmosphere."
Although the book is set in Greenock, no filming has taken place here and the foggy steps have been replaced with a spooky underpass in Wales.
Cathy, who has written 45 books, added: "There are some changes but not that many.
"I have been involved all along the way.
"They have also developed a character called Mrs MacPhail, after me, which I though was really great.
"No location is mentioned in the film and Jonathan Rhys Meyers speaks in his Irish accent.
"I am happy with this, although I would have loved to see it filmed in Greenock."
Panda Eyes, which takes it's name from a specific scene in the film, will debut at the Toronto Film Festival in September next year. It will then be released in cinemas across the world.