After almost an hour's worth of deliberation, the UCI commissaires ruled that the Norwegian would be demoted to the 109th and last place in the peloton. Boasson Hagen had fallen foul of the irregular sprinting rule, having veered over to the left-hand side of the road, blocking out Elia Viviani (Team Sky).
"I was just sprinting for the line," said Boasson Hagen afterward. "I looked down and I know I went over to the left, but it was really not in my purpose to try to block anyone. I did so I'm really sorry for what I did there."
"Viviani was really not happy when he crossed the line, and I expected him to try and protest. Then I thought it was done and I was on the podium so it's a bit of a pity not to have the victory and lose the bonus seconds for GC."
Boasson Hagen, who has won the race twice before in 2009 and 2015, had initially taken the race lead on bonus seconds and had been awarded the green leader's jersey on the podium before learning of the decision.
Despite his disappointment, the versatile sprinter still had his eyes firmly on the goal of adding a third overall win at the race. Should he manage to pull it off, it would be his third stage race victory of the season, after his home races the Tour des Fjords and the Tour of Norway.
"That's my goal, and we'll try to do our best here," he said. "We lost some good seconds today that it would've been nice to have as a bonus. But we just have to keep fighting."