Original: After the destruction of the cathedral the tombstone was lost, but it was found in 1859 (it was being used to cover a well), and is now in the Palais des Beaux Arts museum in Lille.
Simplified: In later years the cathedral was destroyed, and the tombstone was lost, but it was found in 1859 (it was being used to cover a well), and is now in the Palais des Beaux Arts museum in Lille.