From the Independent:
Fears are growing that Notre Dame’s most precious treasure, a relic venerated as the Crown of Thorns worn by Jesus Christ, could have been badly damaged or destroyed in the fire.
The Crown of Thorns, considered Paris’s equivalent of the Crown Jewels, is stored at the end of a nave of the cathedral, not readily visible to visitors. Said to have been worn by Christ before the crucifixion, it is presented to believers for veneration on the first Friday of each month and every Friday during Lent.