In his caption, Nick alluded to him and Carter's "complicated relationship," and stressed that he will "miss his brother more than anyone will ever know."
"I have always held onto the hope, that he would somehow, someday want to walk a healthy path and eventually find the help that he so desperately needed. Sometimes we want to blame someone or something for a loss. But the truth is that addiction and mental illness is the real villain here," Nick captioned the throwback photos he posted.