The Telegraph newspaper is reporting that Johonson was invited to test out the zip line in Victoria Park, London as a "special guest."
Instead of sailing down with the greatest of ease, the mayor was left dangling high above the crowd about 20 meters from the end of the line.
When a spectator asked Johnson how he was feeling, the newspaper quotes him as saying “very, very well thank you,” before shouting: "Get me a rope, get me a ladder" to bystanders.
He tried to reassure the crowd, saying “It’s very, very well organized. It’s going well so far. Right.”
A spokesperson for Johnson told the Telegraph that the Mayor "remained unbowed" by the incident. "The judges will rightly be marking him down for artistic impression,” he joked.
Broadcaster ITV reported that the mayor was pulled to the ground at around 1:30 p.m. local time this afternoon.