pronounced he spoke and ate with difficulty all his life. He did not learn to walk until he was eight and never attended school, but foreign observers noted his mental capacities remained intact; others speculated the Regents overstated his defects to retain political control. It has been suggested Charles suffered from the endocrine disease acromegaly and a combination of rare genetic disorders often transmitted through recessive genes, including combined pituitary hormone deficiency and distal renal tubular acidosis. However, his elder sister did not appear to suffer the same issues and the authors of the most significant study state it has not been demonstrated (his) disabilities...were caused by...recessive alleles inherited from common ancestors. Regardless of the cause, Charles suffered ill health throughout his life, and the Spanish court was split by the struggle between his co-heirs, Louis XIV and Emperor Leopold. His death was expected almost from birth; he was "short, lame, epileptic, senile and completely bald before 35,...repeatedly baffling Christendom by continuing to live." Regency First regency: 1665–1677 Charles was only three years old when Philip died on 17 September 1665, and Mariana was appointed regent, advised by a Regency Council, until he became a legal adult at the age of 14. She adopted the system of using a valido or 'favourite' established by Philip in 1620 and widely used elsewhere in Europe. The first of these was Juan Everardo Nithard, an Austrian Jesuit and her personal confessor who came with her from Vienna; as Philip's will excluded foreigners from the Regency Council, he had to be naturalised, causing immediate resentment. A 'foreigner' herself, the two men habitually identified as her 'favourites' were also outsiders; Nithard was succeeded by Valenzuela, who came from the lower rank of Spanish nobility. Even modern accounts of her reign often reflect contemporary sources that viewed women as incapable of ruling on their own and thus imply a sexual relationship. Mariana used a variety of advisors, including Count Peñaranda and the Marquis de Aytona; historian Silvia Mitchell disputes whether Nithard or Valenzuela were 'validos', since Mariana used them to retain power, rather than delegating it. Despite the emphasis put on her male advisors, she also had female advisors, notably Mariana Engracia Álvarez de Toledo Portugal y Alfonso-Pimentel. Her son's poor health and lack of an heir led to an ongoing struggle between Mariana's 'Austrian' faction, and a 'French' faction, led until his death in 1679