Owain had captured his archenemy, Baron Grey,…

Owain had captured his archenemy, Baron Grey, in an ambush at Ruthin in January 1402, holding him for a year until he receives a substantial ransom from King Henry. (Paying back this debt will effectively ruin de Grey financially.)

Owain's forces in June encounter an army led by Sir Edmund Mortimer, the uncle of the Earl of March, at Bryn Glas in central Wales.

Mortimer's army is badly defeated and Mortimer captured.

It is reported that the Welsh women following Owain’s army killed the wounded English soldiers and mutilated the bodies of the dead, supposedly in revenge for plundering and rape by the English soldiery the previous year.

A great victory for the Welsh rebels, it results in the prolongation of Glyndwr’s revolt and will destabilize English politics for several years to come.

Owain offers to release Mortimer for a large ransom but, in sharp contrast to his attitude to de Grey, Henry IV refuses to pay: as Mortimer could be said to have had a greater claim to the English throne than himself,his speedy release is not an option.

In response, Sir Edmund negotiates an alliance with Owain and marries one of Owain's daughters, Catrin.

Mention of the French and Bretons helping Owain is first heard in this year.

The French are certainly hoping to use Wales as they had used Scotland as a base from which to fight the English.

French privateers begin to attack English ships in the Irish Sea and provide weapons to the Welsh.

French and Breton freebooters are also active in Owain's attacks.