Los Angeles - Ben Affleck once started to build a Batcave in his house.
The star - who was announced last week as the latest actor to portray the iconic superhero - was so obsessed with the character he built a replica of the entrance to the secret lair where Bruce Wayne keeps his alter ego's suit, weapon and vehicles.
Director Kevin Smith - a close friend of Affleck's who has worked with him on several movies - said: "When I first saw his house he was touring me through the place and said, 'Come here, I gotta show you my room'.
"He brings me into the room and goes, 'Look at this'. There's an office room and this beautiful bookcase - he reached under and he clicked something and all of a sudden the bookcase opened.
"I was like, 'No! You built a fucking Batcave?' And he was like, 'No I built a Batcave entrance!' When you went in behind the bookcase it was a panic room."
Ben has always been a huge fan
Affleck has been a controversial choice to play Batman - set to make his debut in the sequel to Man of Steel alongside Superman - but Smith, who has previously written Batman comics for DC, is certain he will do the character justice.
Speaking on the Hollywood Babble-On podcast, he added: "This dude has loved Batman going as far back as I can remember.
"He's always been into the notion. He'll honour the character. I honestly think the dude's a great actor, it makes absolute sense.
"This dude has been to the bottom, then he clawed his way back to respectability ... For him, I think he thinks it's a good move."