Speaking in a behind-the-scenes video featured on the Blu-ray, the actor - renowned for going deep into his roles - discussed his willingness to explore a side of the character nobody had seen before.

"This role has always bee interpreted so beautifully, but then there's the other side," he said. "What else can you uncover?

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He continued: "What other parts of this story or this life, what can you do that hasn't been done? That side of me that likes exploration, that likes adventure, that likes to push the envelope, that was set on fire immediately. I knew that I was going to have to dive really deep and go to a place that I've never gone before."

Leto's previous credits include Requiem for a Dream and Dallas Buyers Club for which he won a Best Supporting Actor Oscar in 2014.

In the clip, director David Ayer said: "During the process of figuring out the Joker and helping Jared create that character, I kinda had to say goodbye to Jared. There was a point when he went away and was replaced slowly and surely by the Joker."