Carney has given a scathing interview to British newspaper The Independent in which, completely unbidden, he attacks Knightley for diva-like antics onset, being a "movie star" as opposed to a "proper" actress and behaving like a "supermodel".
"I didn't enjoy that experience of paparazzi and fabulous openings," Carney said of making Begin Again. "... not that I didn't enjoy Begin Again but Keira has an entourage that follow her everywhere so it's very hard to get any real work done, and so I was very ready to come back to Ireland and make films that nobody cared about who was in it or any of that crap."
"I think the real problem," Carney goes on to explain, "was that Keira wasn't a singer and wasn't a guitar player and it's very hard to make music seem real if it's not with musicians. And I think the audience struggled a little bit with that in Begin Again. And as much as I tried to make it work I think that she didn't quite come out as a guitar-playing singer-songwriter. So I really wanted to work with musicians and actors that could play their instruments properly and sing and stuff like that."
It gets worse. When asked what he took away from making that film, he replied "I learned that I'll never make a film with supermodels again." He goes on to praise Knightley's co-stars in the film - Mark Ruffalo, James Corden and Adam Levine, yes part of his argument is to hold up the lead singer of Maroon 5 as one of the great acting talents of our time, who is "not a bit scared of exposing himself on camera and exploring who he is as an individual" - before re-launching his attack on Knightley.
"I don't want to rubbish Keira," he said, before doing exactly that: "Keira's thing is to hide who you are and I don't think you can be an actor and do that... So it's not like I hate the Hollywood thing but I like to work with curious, proper film actors as opposed to movie stars... It's hard being a film actor and it requires a certain level of honesty and self-analysis that I don't think she's ready for yet and I certainly don't think she was ready for on that film."
Carney is currently promoting his latest film Sing Street, about a young boy in the '80s who statrs a band with his gang of school mates to impress an older girl, which he describes as "a small personal film with no Keira Knightleys in it."
Since Carney's comments went viral this week, several of Knightley's former filmmaker colleagues have rushed to her defence. Directors including Mark Romanek (who worked with Knigthley on dystopian romance Never Let Me Go), Lynn Shelton (the director of Laggies, the family drama Knightley starred in alongside Chloe Grace Moretz) and Lorene Scafaria (Knightley's director on Seeking A Friend For The End Of The World) have called out Carney on his comments and resoundingly praised the actress for her both her work ethic, personality and talent.
So, that's that then. At the very least, I think we can all agree that Keira Knightley is a much better actor than Adam Levine.