Albert's wife, Queen Paola, wiped a tear from her eye as she sat in the Cathedral of St Michael and St Gudula. The ceremony of praise takes place annually on Belgium's national day, which has significantly been chosen as the day his son Prince Philippe will ascend the throne.
Queen Paola wore a bright green dress and matching jacket as she stepped out in Brussels for the historial event with her husband. The king looked visibly excited as he saw signs of thanks being held by supporters and was welcomed into the cathedral by a round of applause.
The royal couple's son, and soon-to-be King of the Belgians, Prince Philippe, also strode to the cathedral in the Sunday sunshine with his wife, Princess Mathilde.
Mother-of-four Mathilde chose an elegant cream dress, which she accessorised with a tan hat and nude heels, as she prepares to become Philippe's Queen consort. Mathilde, 40, is mother to the couple's four children including Belguim's heir, Princess Elisabeth.
King Albert II's daughter, Princess Astrid and his son, Prince Laurent, also attended the church service, taking the time to greet well-wishers on their way to the catherdral.
Once their brother Philippe has been made king, Astrid and Laurent will take on new responsibilites.
Princess Astrid, 51, who is mother to five children, will now fulfil some of the duties previously undertaken by Philippe and Mathilde, including international trips promoting Belgian trade.
Following their appearance at the Te Deum ceremony, the Belgian royals headed to the city's Royal Palace where King Albert officially abdicated and Prince Philippe was sworn in as king.
Just a month after his 79th birthday, King Albert II made an announcement on 3 July that he would abdicate due to age and health reasons.
"Age and health no longer allow me to perform my duties," he said. "After a 20-year reign, the time has come to pass the torch to the next generation."