I recently watched a Spanish TV series on the rise to power and later reign of Isabella I of Castile. In one episode of the first season, set in the late 1460s, she sends a noble ally to meet the Prince of Aragon, Ferdinand, and the Duke of Guyenne (Duke of Berry seems to be the most common name for him in English), brother of King Louis XI of France, and come back to tell her who would be the better husband.
The noble meets with Ferdinand who is this perfect handsome stud warrior prince, and in a following comedic scene, with Guyenne/Berry who is ugly, hunchbacked and/or has some problem with the articulation of his members. Needless to say, he comes back to Castile saying that Ferdinand is the best match, and the rest is History.
The station's webpage has some comments on every episode where its consultants discuss the events in the series and if they are real, fictional or 'enhanced'. In the case of the Duke, they say that his deformity was real, "as proven by paintings of the time", but don't go further. They also say that he spent most of his life plotting and rebelling against his brother until his 'fortunate' early death, possibly by poison.
Isn't that just weird, though? Why would a cripple, unmarried, second son without a heir rebel to dispute the crown to his brother the King?
The Duke's meager Wikipedia page mentions rebeliousness and poisoning (blaming it instead on his mistress' husband) but no deformity. So, what is the truth?
He was not a cripple however he was not a very healthy person.
Charles de France ( his birth name ) was born with a very weak constitution, he was a very thin man ( in a sickly sense ), myope and a bit feeble minded ( so if he was manipulated by someone, it could make sense however I do not know if he really was manipulated ).
He was also very sick at the end of his life. A disease given to him by his mistress, Nicole de Chambres-Montsoreau. He probably died of it the disease ( tuberculosis or syphilis ) so during his last years he must have been very weak physically.
( Sources: French wiki, information I took are written with a source, and a small book/encyclopedia about Kings of France by Jean-Baptiste Santamaria ).