Donny and Marie Osmond opened up about the loss of their brother, Alan, who died on Monday (April 20) at the age of 76.

"This is one of the earliest pictures I have of my brother Alan and me," Donny captioned a childhood photo of the two on his Instagram on Tuesday (April 21). "Even back then, you can see that he had his arm around me, watching over me. That's who he was. My protector. My guide. The one who quietly carried so much responsibility so the rest of us could shine."

The Donny & Marie singer continued, "Alan was our leader in every sense of the word. His tireless work helped build everything we became. I will always be grateful for the sacrifices he made and the love he showed. I owe him more than I can ever fully express."

Brothers Alan, Donny, Merrill, Wayne and Jay formed The Osmonds in the 1960s.

Meanwhile, his sister, Marie, shared her own sweet tribute to her late brother on her Instagram.

"Writing about your sibling's passing is not something easily done," she captioned a photo of a younger Alan. "As his only sister, I know I had a different relationship with him than he had with his brothers, and I must say I loved that! He was always very protective of me but was always there if I needed him. I love you so very much and will miss you dearly."

A spokesperson for Alan's family confirmed to CBS affiliate KUTV and ABC4 Utah that he died on Monday evening. Per KUTV, the singer's wife, Suzanne Pinegar Osmond, and their eight children were at his side when he passed. The outlet also noted that the musician had retired from performing after being diagnosed with multiple sclerosis 40 years ago.