Question: Goodbye Christopher Robin was written by which Guardian Prize winner?

full_context: Document 1: Christopher Robin Milne: Christopher Robin Milne (21 August 1920 – 20 April 1996) was the son of author A. A. Milne. As a child, he was the basis of the character Christopher Robin in his father's Winnie-the-Pooh stories and in two books of poems.
Document 2: Coraline: Coraline is a dark fantasy children's novella by British author Neil Gaiman, published in 2002 by Bloomsbury and Harper Collins. It was awarded the 2003 Hugo Award for Best Novella, the 2003 Nebula Award for Best Novella, and the 2002 Bram Stoker Award for Best Work for Young Readers. It has been compared to Lewis Carroll's "Alice's Adventures in Wonderland" and was adapted into a 2009 stop-motion film directed by Henry Selick.
Document 3: Peter Pan Prize: The Peter Pan Prize was established in 2000 by IBBY Sweden and the Göteborg Book Fair. It is awarded annually "to a book for children or young adults of high quality in both literary and subject terms, satisfying one or more of the following criteria: (1) by an author previously unpublished or little known in Sweden; (2) from a country, language group or culture with limited representation in Sweden; (3) with content concerning children or young adults in less familiar countries and cultures less familiar to Swedish readers"
Document 4: Christopher Robin: Christopher Robin is a character created by A. A. Milne. He appears in Milne's popular books of poetry and Winnie-the-Pooh stories and is named after Christopher Robin Milne, the author's son. The character has subsequently appeared in Disney cartoons.
Document 5: Peter Rabbit (film): Peter Rabbit is an upcoming 2018 3D live-action/CGI animated adventure comedy film written, directed and produced by Will Gluck and co-written by Rob Lieber, based on the stories of the character of the same name created by Beatrix Potter. The film features voice roles played by James Corden, Margot Robbie, Daisy Ridley and Elizabeth Debicki, and live-action roles played by Domhnall Gleeson, Rose Byrne and Sam Neill. The film is scheduled to be released on February 9, 2018. It is not, however, based on the recent British/American CGI-animated TV Series of the same name.
Document 6: Britten's Children: Britten's Children is a scholarly 2006 book by John Bridcut that describes the English composer Benjamin Britten's relationship with several adolescent boys. Bridcut has been praised for treating such a sensitive subject in "an impeccably unsensational tone". The Britten-Pears Foundation described the book as having been "enthusiastically received as shedding new light on one of the most interesting aspects of Britten's life and career, in a study that is thoroughly researched, wonderfully readable and thought-provoking". Bridcut's book followed his television documentary "Britten's Children" shown on BBC2 in June 2004.
Document 7: Paddington 2: Paddington 2 is an upcoming British-French family-comedy film directed by Paul King, co written by King and Simon Farnaby, and produced by David Heyman. It is the sequel to 2014's "Paddington". The film stars Hugh Grant, Brendan Gleeson, Hugh Bonneville, Sally Hawkins, Julie Walters, Jim Broadbent, Peter Capaldi, Madeleine Harris, Samuel Joslin, and the voices of Ben Whishaw and Imelda Staunton. Production began in October 2016, and ended in June 2017. The film is set to release on 10 November 2017.
Document 8: Avril Joy: Avril M. Joy is a British author whose short story "Millie and Bird" won the Costa Short Story Award in the 2012 Costa Book Awards.
Document 9: Goodbye Christopher Robin: Goodbye Christopher Robin is a British film directed by Simon Curtis and written by Frank Cottrell-Boyce and Simon Vaughan. The film stars Domhnall Gleeson, Margot Robbie and Kelly Macdonald, and follows A. A. Milne and his creation "Winnie-the-Pooh". The film was released in the United Kingdom on 29 September 2017.
Document 10: Paddington (film): Paddington is a 2014 comedy film directed by Paul King, written by King and Hamish McColl and produced by David Heyman. Based on "Paddington Bear" by Michael Bond, the film stars Ben Whishaw as the voice of the title character, along with Hugh Bonneville, Sally Hawkins, Julie Walters, Jim Broadbent, Peter Capaldi and Nicole Kidman in live-action roles. The film was co-produced by the French company StudioCanal and the British company Heyday Films. It was released in the United Kingdom on 28 November 2014 and grossed $265.3 million worldwide on a €38.5 million budget. Among several honours, King was nominated for the BAFTA Award for Best Adapted Screenplay and both he and Heyman were nominated for the BAFTA Award for Best British Film. A sequel, "Paddington 2", is scheduled to be released in 2017.
Document 11: Winnie the Pooh (2011 film): Winnie the Pooh is a 2011 American animated buddy musical comedy film produced by Walt Disney Animation Studios and released by Walt Disney Pictures. It is the 51st Disney animated feature film. Inspired by A. A. Milne's stories of the same name, the film is part of Disney's "Winnie the Pooh" franchise, the fifth theatrical "Winnie the Pooh" film released, and Walt Disney Animation Studios' second adaptation of "Winnie-the-Pooh" stories. Jim Cummings reprises his vocal roles as Winnie the Pooh and Tigger, while series newcomers Travis Oates, Tom Kenny, Craig Ferguson, Bud Luckey, and Kristen Anderson-Lopez provide the voices of Piglet, Rabbit, Owl, Eeyore, and Kanga, respectively. In the film, the aforementioned residents of the Hundred Acre Wood embark on a quest to save Christopher Robin from an imaginary culprit while Pooh deals with a hunger for honey. The film is directed by Stephen Anderson and Don Hall, adapted from Milne's books by a story team led by Burny Mattinson, produced by Peter Del Vecho, Clark Spencer, John Lasseter, and Craig Sost, and narrated by John Cleese.
Document 12: Miss Potter: Miss Potter is a 2006 Anglo-American biographical fiction family drama film directed by Chris Noonan. It is a biographical film of children's author and illustrator Beatrix Potter, and combines stories from her own life with animated sequences featuring characters from her stories, such as Peter Rabbit. Scripted by Richard Maltby, Jr., the director of the Tony-winning Broadway revue, "Fosse", the film stars Renée Zellweger in the title role; Ewan McGregor as her publisher and fiancé, Norman Warne; and Lloyd Owen as solicitor William Heelis. Emily Watson stars as Warne's sister, Millie. Lucy Boynton also stars as the young Beatrix Potter. It was filmed in St. Peter's Square Hammersmith, Cecil Court, Osterley Park, Covent Garden, the Isle of Man, Scotland and the Lake District. "Miss Potter" was released on 29 December 2006 so that the film could compete for the 2007 Academy Awards. The film was intended to be released generally on 12 January 2007, but Variety.com reported that the Weinstein Company had decided to push a wider release date until after the Academy Awards on 25 February 2007. The date seemed to fluctuate a number of times, but the Weinstein Company website ultimately listed its release date as 9 March. The film received generally positive reviews and earned Zellweger her sixth Golden Globe nomination.
Document 13: Blue Peter Book Award: The Blue Peter Book Awards are a set of literary awards for children's books conferred by the BBC television programme "Blue Peter". They were inaugurated in 2000 for books published in 1999. The Awards have been managed by reading charity, Booktrust, since 2006. As of 2013, there are two award categories: Best Story and Best Book with Facts.
Document 14: Frank Cottrell-Boyce: Cottrell-Boyce has won two major British awards for children's books, the 2004 Carnegie Medal for "Millions", which originated as a film script, and the 2012 Guardian Prize for "The Unforgotten Coat", which was commissioned by a charity.
Document 15: Millions (2004 film): Millions is a 2004 British comedy-drama film directed by Danny Boyle, and starring Alex Etel, Lewis Owen McGibbon, and James Nesbitt. The screenwriter Frank Cottrell Boyce adapted his novel while the film was in the process of being made. The novel "Millions" was subsequently awarded the Carnegie Medal. This is Danny Boyle's only film not R rated by the Motion Picture Association of America.
ground_truth: Frank Cottrell-Boyce