Newly released letters from Alan Rickman’s personal collection have revealed the actor’s “frustrations” playing the character Severus Snape in the Harry Potter movies.

One letter, written by producer David Heyman, thanks Rickman – who died in 2016 – for working on the second Harry Potter movie, The Chamber of Secrets.

“Thank you for making HP2 a success.” the letter reads. “I know, at times, you are frustrated but please know that you are an integral part of the films. And you are brilliant.”

Rickman later penned a note while working on the 2009 movie The Half-Blood Prince. Titled “Inside Snape’s Head”, the actor writes of frustration over the way director David Yates approached the character’s storyline.

Alan Rickman: Life in pictures Show all 30 1 /30 Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman at the UK premiere of 'A Little Chaos' at ODEON Kensington in London, 2015 Getty Images Alan Rickman: Life in pictures Alan Rickman poses with actress Kate Winslet and actress Helen McCrory as they attend the UK premiere of 'A Little Chaos' at ODEON Kensington in London, 2015 Getty Image Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman signs autographs for fans before the opening ceremony during the Febiofest Prague International Film Festival in Prague, Czech Republic, 2015 Getty Images Alan Rickman: Life in pictures Alan Rickman poses with 'Elle & The Pocket Belles' as he attends on day two of the Qatar Goodwood Festival at Goodwood Racecourse in Chichester, 2015 Getty Images Alan Rickman: Life in pictures Alan Rickman shakes hands with the Queen Elizabeth II during the Dramatic Arts reception at Buckingham Palace, 2014 Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman arrives at the Giffoni Film Festival meeting with the jurors in Giffoni Valle Piana, Italy, 2014 Alan Rickman: Life in pictures 'A Promise' film photocall, 70th Venice International Film Festival, Italy, 2013 Rex Alan Rickman: Life in pictures Alan Rickman walks on the red carpet as he arrives to attend the World Premier for the film 'Gambit' in Leicester Square, in London, 2012 Alan Rickman: Life in pictures (L-R) Alan Rickman, Tom Felton, Emma Watson, Daniel Radcliffe, Rupert Grint and Matthew Lewis attend the New York premiere of 'Harry Potter And The Deathly Hallows: Part 2' at Avery Fisher Hall, Lincoln Center in New York, 2011 Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman attends the 'John Gabriel Borkman' after party at the Brooklyn Academy of Music in New York City, 2011 Alan Rickman: Life in pictures Alan Rickman at the Broadway opening night of 'Seminar' at The Golden Theatre in New York, 2011 Alan Rickman: Life in pictures Actors Sir Christopher Lee (L) and Alan Rickman attend the Royal World Premiere of 'Alice In Wonderland' at Odeon Leicester Square in London, 2010 Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman poses at the Gibson Guitar celebrity hospitality lounge held at the Miners Club during the 2008 Sundance Film Festival in Park City, Utah Alan Rickman: Life in pictures Alan Rickman and Sigourney Weaver attend the photocall for 'Snow Cake' as part of the 56th Berlin International Film Festival (Berlinale) in Berlin, 2006 Alan Rickman: Life in pictures Alan Rickman shares a laugh with Mos Def at the premiere of HBO's 'Something The Lord Made' in New York, 2004 Alan Rickman: Life in pictures Alan Rickman attends the UK Premiere of 'Harry Potter And The Prisoner Of Azkaban' at the Odeon Leicester Square in London, 2004 Alan Rickman: Life in pictures Actor Alan Rickman and Lyndsey Duncan attend the '2002 Tony Award' nominees brunch in New York, 2002 Alan Rickman: Life in pictures Alan Rickman: Life in pictures Alan Rickman and Julia Roberts at 'Hollywood Salutes Bruce Willis: An American Cinematheque Tribute' at the Beverly Hilton Hotel, Beverly Hills, 2000 Alan Rickman: Life in pictures Sigourney Weaver (L), Tim Allen (C) and Alan Rickman (R), pose for the premiere of the science fiction, action comedy film 'Galaxy Quest' outside Mann's Chinese Theatre in Los Angeles, 1999 Alan Rickman: Life in pictures Alan Rickman at the Golden Globe Awards Ceremony in Los Angeles, 1997 Rex Alan Rickman: Life in pictures Alan Rickman with Laim Neeson, Natasha Richardson in 1997 Rex Alan Rickman: Life in pictures Actresses Cybill Shepherd (L) and Christine Baranski (C) present an Emmy to Alan Rickman (R) for outstanding lead actor in a mini-series or special for his lead role in the HBO production of 'Rasputin' during the 48th Annual Emmy Awards in Pasadena, California, 1996 Alan Rickman: Life in pictures Alan Rickman, Emma Thompson and Phyllida Law at the Premiere of "Winter Guest" in Glasgow, Scotland, 1993 Rex Alan Rickman: Life in pictures Alan Rickman, Juliette Stevenson and Michael Maloney in 1990 Rex Alan Rickman: Life in pictures Alan Rickman in 1984

“It’s as if David Yates has decided that this is not important in the scheme of things i.e. teen audience appeal,” he noted.

Rickman’s letters – which also include one from Harry Potter author JK Rowling who thanks the actor for “doing justice to my most complex character” – are going up for auction at the ABA Rare Book Fair in London and have been valued at £950,000.

Other items in the collection include letters from the Prince Charles, Bill Clinton and Tony Blair, along with Rickman’s copy of the Die Hard script, the 1988 blockbuster movie in which he played the villain Hans Gruber.

Actor and bookseller Neil Pearson, who brought together the works, told The Mirror: “It’s a fabulous collection. There are 35 boxes of it – there is the Truly Madly Deeply script in there and Robin Hood Prince Of Thieves is in there.