Diamond was six years old when she caught the world's attention during Kate Middleton and Prince William’s visit to Calgary.
The girl had wanted to meet a princess after watching the royal couple’s wedding from her hospital bed, a dream that was made possible by the Children's Wish Foundation.
Kate is a duchess, not a princess, but the distinction was unimportant to Diamond, who gave the royal couple a bouquet of flowers, a homemade gift and two hugs.
Diamond had a rare form of adrenal cancer. In recent years the cancer had gone into remission, but the disease returned this fall.
Diamond was the inspiration behind an 11-day hockey game to raise money for the Alberta Children's Hospital Foundation, among other causes.
The group's Facebook page posted a message about the girl on Tuesday.
"During her short life, her courage was an inspiration to many," said the post. "We'll miss you, Diamond."