It is a great cultural taboo both in the Seven Kingdoms and the lands beyond the Wall.
Intermarriage between first cousins is actually not considered "incest" in Westerosi society.
A prominent example is that Tywin Lannister married his own first cousin Joanna Lannister, mother of all three of his children.
Alongside kinslaying and the violation of guest right, incest is proscribed by every major religion in Westeros. Cersei Lannister: "The Targaryens wed brothers and sisters for three hundred years to keep bloodlines pure.
The Telegraph reported that dirt caked the surfaces of stoves and cooking facilities, rotten vegetables lay in a refrigerator and a kangaroo was sleeping on one of the children's beds.
Chainsaws, bags of rubbish and exposed electrical wires lay about. But at the time even she did not realise that the 'family cult' was a throwback to a pair of great-great grandparents who were a brother and sister.
Previous DNA testing of King Tutankhamun has revealed the Pharaoh was born from a marriage between sibling.
The boy Joffrey, the boy Tommen, and the girl Myrcella being born of incest between Cersei Lannister and her brother Ser Jaime Lannister, the Kingslayer.
Down through the generations, the family continued to regenerate itself, the children beginning to have sex with one another as soon as they were old enough.
The result, the court documents revealed, was that some of the children seemed developmentally delayed, cognitively impaired or physically handicapped - the shocking result of sex between brothers and sisters, uncles and nieces and fathers and daughters.
By right of birth and blood, I do this day lay claim to the Iron Throne of Westeros.
Let all true men declare their loyalty.""When boys and girls live in the same home, awkward situations can arise.