Tomb slab of an English couple of knights, Marble, 1391

I have been informed by a member of one of the families that it marked a tomb for two Lollard knights, both in service to King Richard II of England. They were Sir John Clanvowe and Sir William de Neville. Clanvowe died 17 October 1391. Sir William de Neville died 19 October 1391, allegedly of a broken heart. Some time before their deaths they had undertaken a "ceremony of wedded brotherhood" no further details are known but it was assumed they had a very close [relationship with each other].
The inscription on the tombstone read Faithful Unto Death.

Wikipedia adds for Lollardy:
"Lollardy, also known as Lollardism or the Lollard movement, was a pre-Protestant Christian religious movement that existed from the mid-14th century to the 16th century English Reformation. It was initially led by John Wycliffe, a Roman Catholic theologian who was dismissed from the University of Oxford in 1381 for criticism of the Roman Catholic Church. The Lollards' demands were primarily for reform of Western Christianity. They formulated their beliefs in the Twelve Conclusions of the Lollards... " and much more.