King Philippe (L) and Queen Mathilde of Belgium take part in the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Veterans take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Helicopters are seen during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

A couple attend the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Veterans take part in the parade during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade on a tank during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Soldiers take part in the parade on a tank during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)

Aircrafts fly during the Belgian National Day celebrations in Brussels, Belgium, July 21, 2019. The Belgian National Day is celebrated on Sunday. (Xinhua/Zheng Huansong)