The drone was being operated by three Korean men aged 42, 39, and 35 who were flying the remote-controlled device around the roof of the 45 meter-high cathedral.
The circulating drone aroused the suspicion of Veneranda Fabbrica, the organization responsible for work and maintenance on the cathedral, who called the police.
When police arrived at the scene they found the three Korean men in the square in front of the cathedral with a remote control. But then things quickly took a turn for the worse.
The three men lost control of their drone, causing it to crash into a construction cable on the cathedral's roof, near a famous golden statue of the Madonna which adorns the cathedral's tallest spire.
While the crash did not sever the cable, it did cause it to become unhooked. According to initial assessments by the Veneranda Fabbrica, the damage is only minor.
The men can perhaps count themselves fortunate not to have seriously damaged the Gothic cathedral, which is the fifth largest in the world and took over six centuries to complete.
Following the crash the police took the men in for questioning during which it emerged that they had come to Milan to give a presentation at the Korean pavilion of the Expo.
The unlucky pilots claimed they had not intended to cause any damage but had only wanted to film some aerial shots of the city, la Repubblica reported.
It is not known what charges, if any, the men will face. Police are still trying to decide if any laws surrounding the use of remote control devices or filming in the city have been violated.