"It is with our deepest regret and sorrow that we now advise you that our sister Kathy Macmillian (Smith) and our brother Bruce Macmillan have both perished in the Napalese earthquake," the family said in a post to the Find Bruce and Kathy Macmillan Facebook page.
Bruce Macmillan's sister told CBC News that Nepalese authorities have not officially confirmed the couple had died, a process that could take weeks. However, given the evidence the family has seen, it is convinced of the couple's fate.
According to the statement on Facebook, the Macmillans were last seen hiking near the village of Chyamki in the Langtang Valley, an area buried in the avalanche.
They had made the decision to take the hiking trip at the last minute, having hiked along that path shortly after they were married 35 years ago.
"Kathy and Bruce passed away while travelling the world, their passion from the moment they were married," the Facebook post says.
The Macmillans had been travelling in Asia for the past six months with their sons, Fraser, 28, and Jay, 30.
Jay Macmillan opted to stay in New Delhi rather than travel to Nepal. Fraser sent a message to an aunt shortly after the earthquake, telling her he was safe but had to run for his life.
"This earthquake has been an enormous tragedy impacting lives across the globe. It has made ours and the world a smaller place."
Fraser Macmillan, who had remained in Nepal to help the search efforts for his parents, has now returned to Edmonton.
The family is planning a public tribute for Bruce and Kathy Macmillan.
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