The 18th century .
Historians assumed Guy to have been a nephew of the first Duke of Athens , Othon de la Roche , but a charter from 1251 , published by J. Longnon in 1973 , establishes him as Othon 's son .
Since the 18th century , historians assumed Guy to have been a nephew of the first Duke of Athens , Othon de la Roche , but a charter from 1251 , published by J. Longnon in 1973 , establishes him as Othon 's son .