[citation needed] De Grey enjoyed the favour both of Richard II and Henry IV, and his chief military exploits were against the Welsh,[7] during the rebellion of Owain Glyndŵr.

On 16 September Owain and brothers had taken up arms and burned Grey's property, for three days the Welsh band ravaged the countryside of Flintshire and Denbighshire.

King Henry IV sent eleven knights to treat with Glyndŵr and then complied with the ransom, ordering the selling of a manor in Kent to raise the monies in mid-1402.

[9] Lord Grey then would have been expected to repay the amount over time as best he could and any outstanding debt would be borne by his family.

[8] Hotspur had refused to surrender a Scottish prisoner, the earl of Douglas, to the King, and had demanded that Edmund Mortimer be purchased his freedom.

[8] The King wrote to Grey and other leading nobles on 23 November 1409, demanding that all officers who were entreating with Glyndŵr should cease forthwith.

The Grey family did in fact sell the Ruthyn Lordship to King Henry VII in 1508 when their fortunes and favour had declined.

[4] Grey was a member of the Council which governed England during the absence of Henry V in France in 1415; he later fought against the French in the Hundred Years War in 1420 and 1421.