Justin Timberlake’s long-time background vocalist Nicole Hurst has reportedly passed away. She was 39.

The pop musician took to his Instagram account on Friday and posted several photos and videos of Hurst, who he frequently referred to as his “sister.”

Featured in the slides were videos of Timberlake and Hurst touring together with the Tennessee Kids. Also in the memories was a selfie of the two as well as clips capturing moments when the two called each other “bro” and “sister.”

“My heart is so heavy. We lost a beautiful soul this week,” Timberlake wrote in the heartfelt tribute. “Nicole lit up every room she walked into. On and off the stage she was a constant source of joy and positivity.”

He continued: “Some things feel so unfair and we will never understand why they happen. What I do know is that we were blessed to laugh with her, to travel with her, and to experience her infectious smile and love for a life filled with music.

Nicole, it’s not enough to say that I am going to miss you dearly. Thank you for your light. I will do my best to carry that with me. I love you, my sister. Forever family and forever a TN Kid. ”