The 59-year-old TV producer shared a heartbreaking tribute to his half-brother via social media on Wednesday.
Shaun Cassidy is remembering all the "extraordinary days" he shared with his late half-brother, David Cassidy.
One day after news broke that David had died at the age of 67 following organ failure and a two-year battle with dementia, Shaun took to Twitter to share a heartbreaking tribute.
"When I was a little boy and my big brother would come to visit, the first call of business would be a punishing pillow fight," he wrote. "During the battle, he would regale me with hysterical stories of our father, often culminating in his taking a giant leap off my top bunk..."
"I tried to catch him of course. I always tried to catch him. But I never could," he continued. "Now, I will carry him, along with all of the funny/sad/extraordinary days we shared, none more filled with love than these last few at his side."
Shaun is the eldest son of Jack Cassidy and Shirley Jones, who played David's onscreen mother on The Partridge Family. In addition to David, Shaun has two other brothers -- Patrick Cassidy, 55, and Ryan Cassidy, 51.
As ET previously reported, David will be cremated, and a private memorial is being scheduled for close family and friends in Los Angeles. A public memorial for a later time is being considered.
He is survived by his 30-year-old daughter, Katie, and 26-year-old son, Beau.
Hear more on David's life in the spotlight in the video below.