“Were mistakes made? Yes,” Bart Johnson wrote while defending sister-in-law Blake Lively on Instagram

Blake Lively’s brother-in-law Bart Johnson is defending her amid controversies surrounding her movie It Ends With Us.

Johnson, who is married to Blake’s sister Robyn Lively, shared a birthday tribute to Blake, 37, on Instagram. High School Musical actor Johnson later responded to one commenter who said it was “disappointing” that Blake appeared to be “promoting happiness in a domestic violence setting without any regard for any victims.”

“I’m really sorry you feel that way. I’m sure you have a huge heart and want the best. I can promise you the truth has not come out yet,” Johnson, 53, wrote in response to the comment. “Blake worked harder on this film than anything I’ve seen her do my entire life. Because it meant so much to her.”

Blake, also a producer of the film, stars as Lily Bloom in the adaptation of Colleen Hoover’s novel, and the story deals with toxic relationships, domestic abuse and other complex themes. There are also reports of tension between Blake and her costar-director Justin Baldoni.

Johnson added in his comment, “The message is in the book. And in the movie. Not in short clips / interviews,” he added in the comment. “She is the reason the message / this movie/ is getting out. Were mistakes made? Yes. I make mistakes in life. But they aren’t under a microscope. Anyway, I respect your views. I got nothing but love for you.”

About tension between Blake and Baldoni, 40, one source told PEOPLE Aug. 13, that the issues behind-the-scenes is more than alleged creative differences between the pair.

“All is not what it seems,” a set source said at that time. “There is much more to this story. The principal cast and [author] Colleen Hoover will have nothing to do with him.”

In a message after It Ends With Us‘ opening weekend, Lively thanked fans on her Instagram Story and shared resources to help domestic violence survivors.

“It Ends With Us is a story of the female experience. All the highest highs, and lowest lows. And we are so proud of it,” she wrote at the time. “We have been in celebration of this film and of getting a message so important out there to the masses. Thank you all for embracing It Ends With Us with the same love, pain and joy we had sharing it with you all.”

Johnson’s birthday post for Blake included a number of photos of the pair together over the years; he explained in a caption to his post that he and Blake first met after Blake’s father, the late Ernie Lively, hired him to teach a teen acting class.

“Countless stories of family trips and vacations, chaperoning her school field trips and MOST important, helping me gain favor of her older sister Robyn (now wife of 25 years) who didn’t know I existed for years after knowing Blake!!” he wrote in his caption. “For 30 years I’ve had the privilege of being fiends with this kind, loving, committed, hard working and inspiring strong [woman]!!”

Robyn, 52, called Blake “one of the best humans I know” in an Instagram tribute for her birthday. She also responded to a commenter who seemed to address the controversy: “Blake is a lovely human being!! I hope she knows that the multitudes of people who love her is so much greater than the negative voices. Happy birthday Blake!!” Robyn wrote back, “Thank you for this.