Many military helicopters and airplanes have been spotted flying over Brussels on Tuesday, prompting many residents to take to social media to find out why.
One Twitter user, who said that he had already spotted several military helicopters, a police helicopter, an A330MRTT, two A400Ms and several F16s, jokingly added that he thought "it was the Russians invading."
Many people posted photos and videos of helicopters flying over, and following a question by a De Standaard journalist, the Belgian Defence Ministry replied that "this is in connection with the rehearsal for 21 July."
On 21 July, Belgium celebrates its National Holiday, marking the anniversary of the inauguration of the country's first king, Leopold I.
In addition to a number of speeches by government officials and the king, festivities and a military and police parade in Brussels, a flypast by the Belgian Air Force is also organised every year.