Since his creation by Bob Crane and Bill Finger in 1939, comic book superhero Batman has proven almost limitless in the things he’s been capable of, even breaking his rule against killing from time to time.

But DC Comics has now drawn the line at what it will allow one of its most prized properties to do.

The US comic book publishers reportedly refused to let the producers of HBO Max adult animated series Harley Quinn include a scene with Batman performing oral sex on Catwoman.

As an adult cartoon series, Harley Quinn is no stranger to material not suitable for children.

So, the reasoning behind DC’s stance?

Harley Quinn co-creator Justin Halpern, speaking to Variety, said DC told him he “absolutely cannot do that” because, for one, “heroes don’t do that”, and secondly, it would be difficult to sell Batman toys if the hero is performing oral sex.

According to Halpern, the producers have far more creative freedom in how they develop and characterise villains, but there are several rules for superheroes.

The discussion around the oral sex scene took place during production of the upcoming third season of Harley Quinn, which streams later this year.