Joker is well on its way to becoming one of the biggest comic book movies of all time, and filmmaker Todd Phillips has shared an extensive behind-the-scenes look at the making of the film.

Phillips posted photos from an early makeup test with star Joaquin Phoenix, along pictures of himself and the actors on-set between filming takes for the gritty thriller. Intriguingly, one of the images is a closer glimpse at the notebook kept by Arthur Fleck, where he scribbled his disturbing thoughts and jokes.

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The look at Arthur's diary includes a twisted take on the iconic Batman supporting character Catwoman, with a scantily clad woman seen riding a large feline, a psychosexual glimpse into Arthur's warped psyche.

Expected to earn $1 billion at the worldwide box office before the end of its theatrical run, Joker has become one of the biggest movies of the year, made all the more impressive by its R-rating, gritty tone and relatively low production budget.

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Directed by Todd Phillips, Joker stars Joaquin Phoenix, Robert De Niro, Zazie Beetz, Bill Camp, Frances Conroy, Brett Cullen, Glenn Fleshler, Douglas Hodge, Marc Maron, Josh Pais and Shea Whigham. Joker is now in theaters.