King Tut married his sister, Bobbi Kristina with adopted brother and Game of Thrones incest couple[GETTY/FLYNET/PH]

In Ancient Egypt the practice was not frowned upon and royalty would often marry members of their own family in a bid to preserve their royal lineage. In fact, historians believe that the practice was common in all classes of Egyptian society. Besides being the son of Akhenaten and an unidentified sister-wife, Tut is also said to have married his own half-sister, Ankhesenamun. Another famous historical figure who married within her own family was Cleopatra, who was wed to her younger brother Ptolemy XIII before she became involved with either Julius Caesar or Mark Antony. While incest remains illegal and one of the most widespread cultural taboos worldwide, there are however many more recent examples of famous people who have engaged in romantic liaisons with family members. Among them was Albert Einstein who married his second cousin Elsa in 1919, soon after his divorce from his first wife Mileva.

Einstein married his second cousin Elsa [Getty Images]

A common justification given for the incest taboo is the impact inbreeding may have on children of incestuous sex. Children whose biological parents have a close genetic relationship have an increased risk of congenital disorders, death and disability as similar immune systems may be more vulnerable. Ironically Charles Darwin, who popularised the theory of evolution, married his first cousin Emma Wedgwood. They had ten children together, two of whom died in infancy and another who passed away aged ten. There is evidence to suggest that Darwin feared his children may have inherited weaknesses from inbreeding because of his close family ties to his wife. He examined this topic in his writings, contrasting it with the advantages of crossing amongst many organisms.

Darwin had ten children with his wife who was his first cousin [Getty Images]

Europe's royalty is also known for historic inter-familial relationships. Records show that the Spanish Habsburg kings frequently engaged in consanguineous marriage (between biological relatives). Nine of the 11 marriages that occurred over the dynasty's 200-year reign were consanguineous, with two uncle-niece marriages and one first-cousin marriage. The world of showbiz has also had its fair share of incest scandals. Fifties rock and roll star Jerry Lee Lewis married his 13-year-old cousin Myra. His career was seriously damaged by the scandal and never quite recovered. The couple had two children together, one of whom died aged three. Woody Allen split from his long-term partner Mia Farrow after it emerged that he had taken naked photographs of her adopted daughter Soon-Yi. Allen went on to marry Soon-Yi Previn, who was often referred to as his stepdaughter - though he never actually adopted her.

Woody Allen and wife Soon-Yi, who is his former partner's adopted daughter [EPA]

In the wake of Whitney Houston's death, it emerged that her daughter Bobbi Kristina had got together with her secret son, Nick Gordon. However, the pair are not blood relatives as Gordon was adopted by Houston.

Whitney Houston's daughter Bobbi Kristina with her adopted brother Nick Gordon [FameFlynet.uk.com]

Franklin D. Roosevelt and wife and Eleanor were second cousins, as were Queen Victoria and Prince Albert. New York City Mayor Rudolph Giuliani was also briefly married to a second cousin.

Former New York mayor Rudolph Giuliani was briefly married to a second cousin [PNP/Wenn]

Game of Thrones' characters Jamie and Cersei Lannister [HBO]