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

Context paragraphs:
Serializer: serializer.net was an online artist collective that was active from 2002 to 2012.  Serializer included many well-known award-winning alternative artists like Tom Hart (Xeric Award winner), Eric Millikin (Pulitzer Prize winner), Shaenon K. Garrity (Lulu Award winner), James Kochalka (Eisner Award winner), Dean Haspiel (Emmy Award winner), Howard Cruse (Prix de la critique winner), Chris Onstad (Ignatz Award winner), Nick Bertozzi (Harvey Award winner), and Jen Sorenson (Herblock Prize winner).  Each artist created, and sometimes collaborated on, serialized webcomics.

When We Were Very Young: When We Were Very Young is a best-selling book of poetry by A. A. Milne.  It was first published in 1924, and was illustrated by E. H. Shepard.  Several of the verses were set to music by Harold Fraser-Simson.  The book begins with an introduction entitled "Just Before We Begin", which, in part, tells readers to imagine for themselves who the narrator is, and that it might be Christopher Robin.  The 38th poem in the book, "Teddy Bear", that originally appeared in "Punch" magazine in February 1924, was the first appearance of the famous character Winnie-the-Pooh, first named "Mr. Edward Bear" by Christopher Robin Milne.  In one of the illustrations of "Teddy Bear", Winnie-the-Pooh is shown wearing a shirt which was later colored red when reproduced on a recording produced by Stephen Slesinger.  This has become his standard appearance in the Disney adaptations.

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.

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.

Nuala Quinn-Barton: Nuala Quinn-Barton (formerly London model) is an Independent film producer and talent Manager.  She is best known for producing films such as "Homecoming" (2009), "The Third Half" (2012), "Goodbye Christopher Robin" (2017), and for managing the career of her daughter Mischa Barton.

John Christopher: Sam Youd (16 April 1922 – 3 February 2012), known professionally as Christopher Samuel Youd, was a British writer, best known for science fiction under the pseudonym John Christopher, including the novels "The Death of Grass", "The Possessors", and the young-adult novel series "The Tripods".  He won the Guardian Prize in 1971 and the Deutscher Jugendliteraturpreis in 1976.

Christopher Nicole: Christopher Robin Nicole (born (1930--)7 1930 ) is a prolific British writer of over 200 novels and non-fiction books since 1957.  He has written as Christopher Nicole and also under several pseudonyms including Peter Grange, Andrew York, Robin Cade, Mark Logan, Christina Nicholson, Alison York, Leslie Arlen, Robin Nicholson, C.R. Nicholson, Daniel Adams, Simon McKay, Caroline Gray and Alan Savage.  He also wrote under the pen name Max Marlow when co-authoring with his wife, fellow author Diana Bachmann.

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.

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.

Paula MacArthur: Paula MacArthur was born in Enfield, England in 1967.  MacArthur was joint first prize winner in 1989 of the ‘John Player Portrait Award’ at the National Portrait Gallery, London with Tai-Shan Schierenberg.  In 1993 she graduated from the Royal Academy of Arts where she was awarded the ‘Royal Academy Schools Prize for Painting’, that same year she was a prize winner of ‘Liverpool John Moores 18’.  Her work is held in numerous collections including The National Portrait Gallery, London the collection of Baron and Baroness von Oppenheim and The Priseman Seabrook Collection.

Supporting paragraphs: Goodbye Christopher Robin Frank Cottrell-Boyce
Answer: Frank Cottrell-Boyce