Alan Rickman's secret journals explain why he decided to keep playing Severus Snape while battling cancer

Secret diaries written by the late Harry Potter star Alan Rickman have revealed why he decided to keep playing Snape following his diagnosis with prostate cancer.

Rickman, who starred in the fantasy series from 2001 to 2011, documented details about his career and home life in 26 journals from 1992.

It was previously announced that the dairies would be published in October by Henry Holt & Company, but early excerpts released this weekend document his experience playing Snape.

Alan Rickman agreed to play Snape in 2000.

Warner Bros.

In his diaries, published by The Guardian, Rickman recalls the moment he accepted the role in Harry Potter on 23 August, 2000, writing simply: "6.30pm Pile into the car and drive to Siena to get to Il Campo before dark. To the Patio Bar where, around 8pm, I called LA and said OK to HP [Harry Potter]."

It's a small note for a franchise that went on to change the world, and even the following day Rickman admitted he was 'feeling a bit nothing about HP', adding: "which really disturbs me – or is it because I’m reading Martin Amis’s Experience which charts A Life …"

Rickman described 21 September, 2000, as the day 'Harry P takes off', and he went on to create four movies before being diagnosed with prostrate cancer.

His diagnosis came before production began on Harry Potter and the Order of the Phoenix, and it was decided that Rickman's best option would be to remove the entire prostate; a procedure he underwent at the Vanderbilt University Medical Center in Nashville, Tennessee.

Rickman was diagnosed with cancer before production on the fifth Harry Potter film.

Everett Collection Inc/Alamy Stock Photo

In a diary entry from 5 January, 2006, Rickman describes how he woke up and was driven to the hospital for a pre-op, writing: "This is like a film set. Nothing seems real. Remembering nothing but with that painkiller high in the recovery room. Attentive, caring people."

On 30 January, Rickman 'finally' said yes to the fifth Harry Potter film.

Explaining his decision to continue starring as Snape, he wrote: "The sensation is neither up nor down. The argument that wins is the one that says: 'See it through. It’s your story'."

His experiences appear to have taken a toll on him as Rickman describes himself as being quieter than ever before when he returned to set - and not just in the dark, moody way that comes with Snape's mysterious character.

Snape died in the final Harry Potter film.

Warner Bros.

On 12 April, 2006, he wrote: "I realise as soon as that [Snape’s] ring and costume go on – something happens. It becomes alien to be chatty, smiley, open. The character narrows me down, tightens me up. Not good qualities on a film set. I have never been less communicative with a crew. Fortunately, Dan [Radcliffe] fills that role with ease and charm. And youth."

Rickman survived to complete his role as Snape, with his final appearance coming in Harry Potter and the Deathly Hallows - Part 2, when his character dies.

The actor himself passed away in 2016, five years after the Harry Potter series came to an end.

If you’ve been affected by any of these issues and want to speak to someone in confidence, contact Macmillan’s Cancer Support Line on 0808 808 00 00, 8am–8pm seven days a week