In the early 15th century during the Owain Glyndŵr revolt in Wales against the new King Henry IV the building was under a very real threat from Welsh forces.

Tretower Castle was listed as a defensible stronghold for the King in 1404 and under Sir James Berkeley successfully held off an attack.

The Welsh forces retreated down the valley of the River Usk but laid an ambush for the pursuing English and engaged them in a skirmish below Craig-y-Dorth hill near Mitchel Troy, where the large fields are still referred to as Upper and Lower Battlefield.

According to the Annals of Owain Glyn Dwr, "Here the more part of the English were slain and they were chased up to the town gate [of Monmouth]".

In early times the castle was held by the Picard (Pychard) family who gained extensive lands in Herefordshire for assisting William the Conqueror.

Sir Roger Vaughan was to become the richest Commoner in Wales at the height of his career [citation needed] and he immediately set about refurbishing and developing Tretower Court into one befitting a prosperous man and leaving us the building that broadly speaking we see today.

He also added a new west range, immediately doubling the accommodation available, building a brand new hall, solar and upper rooms.

The property was sold in 1783 as the Vaughan family decided to take up occupancy at another of their properties following a marriage and Tretower Court passed out of Vaughan hands to a series of new tenants and over time some previously residential rooms were adapted as stores, barns and then even used by animals, part even becoming a piggery.