Family: 7th Earl of Mar Domhnall I of Mar / Helen Ferch Llywelyn (F1968)
The parent family of Lady Isabella of Mar is the Family.
5th Earl of Mar William of Mar (1235-1281) 
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| Prince Of North Wales Llywelyn Ap Iorwerth (1173-1240)
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Princess of Wales and Lady of Snowdon Joan (1191-1237)
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Princess Gwladus Ferch Llywelyn (1206-1251)  |
| Prince of Gwynedd Dafdd Ap Llywelyn (1215-1246) |
| 7th Earl of Mar Domhnall I of Mar (1243-1302)
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| Helen Ferch Llywelyn (1206-1253)
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 | Lady Isabella of Mar (1227-1301) |
| 8th Earl of Mar Garnait of Mar ( -1305) |
