Wellington computer analyst-programmer Mike Butler walked 2325 kilometres around the South Island in 69 days with border collie Rapid and kelpie Ella last year, raising more than $22,000.
An electrical fault caused a fire in his Island Bay home on Sunday morning, killing seven-year-old Rapid, which was recovering from a tear in a cruciate ligament, Butler said.
"He was resting in a crate recovering from surgery."
Butler was judging a dog agility competition in Upper Hutt, something he would normally take Rapid along to, when he got the phone call from police about 7.30am on Sunday.
"I'm absolutely devastated. I'm barely hanging in there. He was something special. For seven years he's been my shadow, my sports partner. He cuddled up with me at night." MORE>>