Cassidy's rep confirmed on Tuesday that Cassidy had died at age 67.
Hollywood is mourning the death of David Cassidy.
"On behalf of the entire Cassidy family, it is with great sadness that we announce the passing of our father, our uncle, and our dear brother, David Cassidy. David died surrounded by those he loved, with joy in his heart and free from the pain that had gripped him for so long," Cassidy's rep told ET in a statement from the family. "Thank you for the abundance and support you have shown him these many years."
Stars took to social media to pay tribute to Cassidy, with Brian Wilson reminiscing about the time they spent together at the beginning of their careers.
"I’m very sad to hear about David Cassidy," Wilson tweeted. "There were times in the mid-1970s when he would come over to my house and we even started writing a song together. He was a very talented and nice person. Love & Mercy to David and his family."
Cassidy's nephew, Jack Cassidy, who competed on The Voice earlier this year, wrote, "My uncle David Cassidy has sadly passed away tonight... & in the process of mourning I can't help but thank God for the joy that he brought to countless millions of people! I don't think I'm alone in saying that we will all miss him. God Speed!"
"So sorry to hear about David Cassidy's passing. Godspeed," Rick Springfield tweeted.
See more reactions below.