Frances Conroy is reportedly set to join the cast of the Joker standalone movie.

The 'American Horror Story' star could star alongside Joaquin Phoenix, who is playing the notorious villain in the highly anticipated Warner Bros. and DC film.

The 64-year-old actress would play the Joker's mother, a woman called Penny - and this will be the stars latest DC Comics movie role after playing Ophelia Powers in the 2004 Halle Berry-led 'Catwoman' movie.

Robert De Niro,74, is also suspected to be cast in the film as a talk show host essential in the rise of the titular villain.

The project has a budget of $55 million - which is smaller than most of its kind - and the movie will be loosely based on the origin story for the character depicted in Alan Moore's 'The Killing Joke'.

Meanwhile, Joaquin recently teased that his portrayal of the villain - known for his pale face and scary red lips - would be ''unique''.

The 43-year-old actor said: ''I wouldn't quite classify this as like any genre. I wouldn't say it's a superhero movie, or a studio movie or a ... It feels unique, and I think more then anything, and probably the most important thing, is Todd [Phillips, the director] seems very passionate about it and very giving, and so that's exciting.

''I think, underneath the excitement of these films, and the size of them, there are these incredible characters that are dealing with real life struggles.

''And sometimes that is uncovered and exposed, and sometimes it isn't, and so I always felt, like, there were characters in comics that were really interesting and deserve the opportunity to be kind of studied. And so I think that's what Todd sees appealing about this idea.''