Philip I, Landgrave of Hesse, and soon began to take part in Imperial business. Heir apparent On 13 September 1548 Emperor Charles V married Maximilian to Charles's daughter (Maximilian's cousin) Maria of Spain in the Castile residence of Valladolid. By the marriage his uncle intended to strengthen the ties with the Spanish branch of the Habsburgs, but also to consolidate his nephew's Catholic faith. Maximilian temporarily acted as the emperor's representative in Spain, however not as stadtholder of the Habsburg Netherlands as he had hoped for. To his indignation, King Ferdinand appointed his younger brother Ferdinand II administrator in the Kingdom of Bohemia, nevertheless Maximilian's right of succession as the future king was recognised in 1549. He returned to Germany in December 1550 in order to take part in the discussion over the Imperial succession. Maximilian's relations with his uncle worsened, as Charles V, again embattled by rebellious Protestant princes led by Elector Maurice of Saxony, wished his son Philip II of Spain to succeed him as emperor. However, Charles' brother Ferdinand, who had already been designated as the next occupant of the imperial throne, and his son Maximilian objected to this proposal. Maximilian sought the support of the German princes such as Duke Albert V of Bavaria and even contacted Protestant leaders like Maurice of Saxony and Duke Christoph of Württemberg. At length a compromise was reached: Philip was to succeed Ferdinand, but during the former's reign Maximilian, as King of the Romans, was to govern Germany. This arrangement was not carried out, and is only important because the insistence of the emperor seriously disturbed the harmonious relations that had hitherto existed between the two branches of the Habsburg family; an illness that befell Maximilian in 1552 was attributed to poison given to him in the interests of his cousin and brother-in-law, Philip II of Spain. The relationship between the two cousins was uneasy. While Philip had been raised a Spaniard and barely travelled out of the kingdom during his life, Maximilian identified himself as the quintessential German prince and often displayed a strong dislike of Spaniards, whom he considered as intolerant and arrogant. While his cousin was reserved and shy, Maximilian was outgoing and charismatic. His adherence to humanism and religious tolerance put him at odds with Philip who was more committed to the defence of the Catholic faith. Also, he was considered a promising commander, while Philip