Heath Ledger's Joker diary acts as a disturbing reminder of his commitment to the role

A diary revealed the incredible, and somewhat harrowing, dedication Heath Ledger put into playing the Joker.

Just months before he tragically passed away at just 28, Ledger was busy filming 2008’s The Dark Knight - for which he was posthumously awarded an Academy Award for Best Supporting Actor.

Following his untimely death, German filmmaker Dag Freyer set about making a documentary: Too Young to Die: Heath Ledger, charting his demise - and in the process came across his personal ‘Joker Diary' he made while preparing for the role. You can watch a clip from the documentary here:

It contained notes and inspirations behind his acting choices, revealing a plethora of terrifying muses including hyenas, clowns, comic strips and Alex DeLarge from Stanley Kubrick's cult classic, A Clockwork Orange.

The diary was shared by Heath's dad, Kim Ledger, who confirmed that his son put himself into a self-imposed exile to really delve into the Joker's chilling psyche.

"He pretty well locked himself up in a hotel room for weeks. He galvanised the upcoming character. That was typical of Heath. He would do that. He liked to dive into his characters, but this time he really took it up a notch," Kim said.

Warner Bros.

One chilling page of the diary has the words, 'BYE BYE' scrawled in large, seemingly uncontrolled letters.

Ledger had finished his work for The Dark Knight in October 2007, however, the crew was in the process of editing when he died.

A coroner concluded that Ledger died due ‘acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine'.

His death was ruled an ‘accident’ and was said to have been a result of 'the abuse of prescribed medications', combined with a possible chest infection that stopped him breathing.

Broadview Pictures

Commenting on his passing, The Dark Knight director Christopher Nolan said: "It was tremendously emotional, right when he passed, having to go back in and look at him every day.

"But the truth is, I feel very lucky to have something productive to do, to have a performance that he was very, very proud of, and that he had entrusted to me to finish."

Some people claimed that the twisted psyche of the Joker somehow played a role in his death, but that was shut down by his co-star Christian Bale, who recalled Heath saying: "[The Joker was] the most fun I've ever had, or probably ever will have, playing a character."