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(KTLA) – After the death of Aaron Carter at his Southern California home on Saturday, the family of the pop star paid tribute to him on social media.

Carter, 34, was found dead at his house in Lancaster on Saturday. Authorities said a house sitter found him in the bathtub, and resuscitation efforts were unsuccessful.

The death of Carter, who was diagnosed with multiple mental illnesses and struggled with addiction, is under investigation by the Los Angeles County Sheriff’s Department.

Despite their rocky relationship — Aaron claimed his family was trying to put him into a conservatorship against his will — older brother and Backstreet Boy Nick Carter and twin sister Angel Conrad shared their love for Aaron.

“To my twin… I loved you beyond measure,” Conrad wrote on Instagram Saturday. “You will be missed dearly. My funny, sweet Aaron, I have so many memories of you and I, and I promise to cherish them. I know you’re at peace now. I will carry you with me until the day I die and get to see you again.”

Older brother Nick Carter expressed similar feelings on Twitter. The brothers, both pop stars, sometimes worked together, with Aaron opening for the Backstreet Boys on tour.

That relationship, however, was strained at times, with E! reporting about a year ago that Nick and his wife, Lauren Kitt, hadn’t spoken to Aaron in years.

Nick Carter acknowledged the “complicated relationship,” though he added that his “heart is broken” as “my love for him has never ever faded.”

“I have always held on to the hope that he would somehow, someday want to walk a healthy path and eventually find the help that he so desperately needed,” Nick wrote on Twitter. “Sometimes we want to blame someone or something for a loss, but the truth is that addiction and mental illness are the real villains here. I will miss my brother more than anyone will ever know. I love you baby brother.”

Aaron was preceded in death by his sister and fellow singer Leslie Carter, who died of a drug overdose in 2012. She was 25 years old.