The Chapel of Our Lady of the Chaste King was built by order of Bishop Tomás Reluz in 1705, over another chapel founded by Alfonso II the Chaste in the 9th century, and is structured parallel to the cathedral, forming a separate temple with its own exterior entrance through a garden located to the left of the cathedral. It is the work of Bernardo de Haces and Luis de Arce.

It is joined to the cathedral by the great doorway by Juan de Malinas, built between 1470 and 1485 in the late Gothic style. The door is divided in two by a mullion in which is sculpted the figure of the Virgin and Child flanked on the sides of the doors by the figures of the apostles St. James and St. Peter and on the right St. Paul and St. Andrew. On the side, to the left of the door and before entering the chapel, a stone inscription of Alfonso III the Great can be seen.

Some Asturian kings were buried in this chapel. It was the first pantheon of the Spanish monarchy. On the pendentives of the main arches there are busts of several Asturian kings.

In the north nave there is a fine altarpiece of the Virgin of the Light from the 16th century, from the school of Juan de Juni. Next to it, there are four small apostles; in the attic is the figure of God the Father. It also has two marble images of Saint Peter and Saint Paul from the 18th century. It was customary to turn the key of St. Peter to open the gates of heaven for the soul.

Inside the chapel is the Pantheon of Kings of Oviedo Cathedral, in the centre of which is the tomb of Ithacius, with a 5th century tombstone.