On that day, whilst celebrating mass, the parish priest of Ittre found a fragment of the consecrated host in the corporal, which, when he took it in his hands, began to bleed.

The small Gothic chapel built over the site of the miracle, which is still the priory church, is the oldest building of the complex and is surmounted by an elegant bell tower.

It has a 16th-century ceiling, decorated stalls, paintings of the miracle (by J. Crockaert, 1777), a double-naved sacristy, a polychrome statue of the Virgin and Child, a reliquary and a monstrance.

The local population intervened and although the cloister was demolished and part of the buildings turned into a farm, the chapel survived and was served by a chaplain throughout the 19th century.

In 1921 the canons were allowed to return to Mondaye and handed over Bois-Seigneur-Isaac to their co-brothers of Averbode Abbey, who ensured the continuity of monastic life and pastoral services there.