According to Expatica:
King’s Day traditionally includes a Te Deum mass… The celebration takes place in the Saint Michael and Saint Goedele cathedral in central Brussels…
…the retired King Albert and his wife Queen Paola attended the mass… In his address, the Arch Bishop…talked about the role that King Filip will play, claiming the king is facing a very complicated task in a country divided by different regions (Flanders, Brussels and Wallonia) and language communities (Dutch, French and German).
King Albert and Queen Paola were welcomed by some 100 fans outside the cathedral, which gave them great pleasure.