In a major blow to the integrity of the Iditarod dog-sled race, officials for the sport on Monday identified the four-time champion Dallas Seavey as the musher whose dogs recently tested positive for banned drugs in this year’s competition.

Seavey, whose family is full-fledged Iditarod royalty, had his string of three consecutive victories in the annual race, which runs through the Alaskan wilderness, broken in March by his father, Mitch. Father beat son by a little less than three hours and in the process broke Dallas Seavey’s world record, which had been set in 2016.

Earlier this month, the Iditarod Trail Committee made the surprising announcement that four of the dogs in this year’s event had tested positive for the opioid pain reliever Tramadol. It was the first time dogs had tested positive for a prohibited substance since the race began testing in 1994.

Despite the positive test, the committee said Seavey would be allowed to participate in next year’s race and would not face any discipline because of what it called an “ambiguous rule” that requires them to establish the musher’s intent. But in a Facebook post, Seavey linked to a lengthy statement he made in a YouTube video and said he had withdrawn his name from the 2018 competition in protest.