He was still a child at the death of his father Gruffydd Fychan in 1289, so that he lands were placed in the custody of the queen and then of Reginald de Grey, Justice of Chester and then Thomas of Macclesfield. Madog ap Gruffydd asked the king for a suitable provision to be made for him, and seems to have been granted his father"s lands.
He is sometimes described as Madog III of Powys Fadog. However, he was only lord of some of the family lands under the English crown. These apparently consisted of Glyn Dwfrdwy in Edeirnion and half of the commote of Cynllaith, comprising the area around Sycharth.
Madog married Gwenllian, daughter of Ithel Fychan of Halkin and had a son Gruffydd of Rhuddallt, who was married on 8 July 1304 at the age of six to Elizabeth, daughter of John LeStrange of Knockin.
Madog died circa 1304/1306 in his manor of Rhuddallt, probably in Glyn Dyfrdwy. In 1956 the heraldic tomb slab of Madog was found at the Abbey and is now on display there.
lieutenant is said to be the best preserved example of a stone monument in North Wales from this period. The carving shows a shield with a lion rampant, surrounded by the inscription in the upper half of the slab.
A sheathed sword is diagonally set behind the shield and a spear runs vertically along the slab.
The whole is decorated with vine leaves and bunches of grapes. The inscription reads:
HIC IACET: Master of Arts/DOC": FIL": GRIFINI: DCI: VYCHAN
This translates as: Here lies Madog son of Gruffydd called Fychan
Gruffydd of Rhuddallt became a ward of his father in law, who died in 1309. Custody of his lands was then granted to Edmund Hakluyt, who sold the wardship to Roger Mortimer of Chirk.
However, he probably stayed with the LeStrange family, as Roger Mortimer disputed the validity of the marriage in 1305.
Gruffydd ultimately obtained possession of his lands in March 1321. He held the two lordships by Welsh barony (pennaeth), which required him to serve in the king"s army with his men at the king"s expense.
He died sometime after 1343. However, some genealogical tables insert another generation with a Madog Fychan as son of Madog Crypl.
