D. Lopo Dias de Sousa, seventh and last religious Master, Canon of the Order of Christ, began his mastery in 1373 which lasted until he passed away.

In 1384, even though he is D. Leonor Teles´ nephew, he sides with the Avis Master and takes the Knights of Christ to join D. Nuno Álvares Pereira´s army and the Avis Master militia in order to defend the Portuguese sovereignty being challenged by the Castilian king. He was taken prisoner during the assault of Torres Novas - then occupied by the Castilians - is freed after the Aljubarrota battle and considered a war hero. After victories in battles that placed the Avis Master on the Portuguese throne, D. Lopo will constantly accompany the king wherever he goes. When King John weds D. Filipa of Lancaster, he appoints D. Lopo as his wife´s equerry.

D. Lopo becomes a very close friend of the Royal Household, especially of Infante D. Henrique, who aided him in the conquests in North Africa. His dedication to the Avis House will lead to the Order of Christ being linked to the Portuguese monarchy. Upon his death, the king got from the Pope the nomination for the Infante as Regent and Governor of the Order- as secular master. By order of the Infante, his body is transferred to the Templar Rotunda. His tomb is currently in the northern side, close to the corridor that connects the church to the Cemetery Cloister.