Japanese authorities are investigating a possible threat against the country’s 12-year-old prince, after a pair of knives were discovered near the boy’s school desk — a week before he is set to become second in line to the throne.

Prince Hisahito, the grandson of Emperor Akihito, was in another part of the building at Ochanomizu University when officials believe the knives were planted on Friday, Kyodo News reported.

The blades of the weapons were painted pink, and the hilts were attached to a stick, with one end on the prince’s desk and the other on the desk next to his, so the knives were suspended above the ground.

The person who planted the blades was able to identify the prince’s seat from the name tags on each desk.

The young royal is usually guarded by police officers, but they do not accompany him inside school classrooms, according to the outlet.

Surveillance footage shows a man dressed in blue and wearing a helmet trespassing on school property that day. Police believe he posed as a construction worker to gain access.

Prince Hisahito’s father, Crown Prince Naruhito, is set to take over for Emporer Akihito Tuesday, after 30 years on the throne. The royal family holds no ruling power.