The 'Gossip Girl' star leads the cast of the new film - based on the novel of the same name by Colleen Hoover - but she's been targeted by online rumours suggesting she's locked in a bitter feud with her director and co-star Justin Baldoni after a number of disagreements during the shoot.
Now Brandon - who appears alongside the pair in the film - has told the haters to back off because its a "distraction" from the movie's important issues about domestic violence. In a post on Instagram, he wrote: "I wanted to take a minute and address all this stuff swirling online.
"Colleen and the women of this cast stand for hope, perseverance, and for women choosing a better life for themselves. Vilifying the women who put so much of their heart and soul into making this film because they believe so strongly in its message seems counterproductive and detracts from what this film is about. It is, in fact, the opposite of the point."
He went on: "What may or may not have happened behind the scenes does not and hopefully should not detract from what our intentions were in making this film. It's been disheartening to see the amount of negativity being projected online ...
"There isn't a single person involved in the making of this film that was not aware of the responsibility we had in making this. A responsibility to all the women who have experienced generational trauma - domestic abuse - or struggle with looking in the mirror and loving who they see."
Brandon went on to call the movie a "harsh reality check for the men who need to get their s*** together and take responsibility for themselves and their actions" adding its aim is to "spread love and awareness".
The actor added: "It is not meant to once again, make the woman the 'bad guy', let's move beyond that together. All I ask is that before you spread hate on the internet, ask yourself who its helping.
"Ask yourself if your opinions are based in any fact. Or if you simply want to be a part of something. Let's be a part of something better together. A part of a new story being written for women and all people everywhere."