Question: The queen of Castile, Joanna of Castile, married this member of the house of Habsburg who was the son of which monarch?
Context: The Council of Castile (Spanish: Real y Supremo Consejo de Castilla ), known earlier as the Royal Council (Spanish: Consejo Real ), was a ruling body and key part of the domestic government of the Crown of Castile, second only to the monarch himself.  It was established under Queen Isabella I in 1480 as the chief body dealing with administrative and judicial matters of the realm.  With the 1516 ascension of King Charles I (later Holy Roman Emperor Charles V) to the throne of both Castile and Aragon, the Royal Council came to be known as the Council of Castile because Charles was king of many dominions other than Castile, while the Council retained responsibility only over Castile. Philip I (22 July 1478 – 25 September 1506) called the Handsome or the Fair, was the first member of the house of Habsburg to be King of Castile.  The son of Holy Roman Emperor Maximilian I, at the age of three Philip inherited the greater part of the Duchy of Burgundy and the Burgundian Netherlands (as Philip IV) from his mother, Mary, and at 27 briefly succeeded to the Crown of Castile as the husband of Queen Joanna, who was also heir presumptive to the Crown of Aragon.  He was the first Habsburg monarch in Spain.  He never inherited his father's territories or became Holy Roman Emperor because he predeceased his father, but his son Emperor Charles V eventually united the Habsburg, Burgundian, Castilian, and Aragonese inheritances. John I (Spanish: "Juan I" ; 24 August 1358 – 9 October 1390) was King of the Crown of Castile from 1379 until 1390.  He was the son of Henry II and of his wife Juana Manuel of Castile.  He was the last monarch of Castile to receive a formal coronation. Isabella, Princess of Asturias (2 October 1470 – 23 August 1498) was a Queen consort of Portugal and heir presumptive of King Ferdinand II of Aragon and Queen Isabella I of Castile, as their eldest daughter.  Her younger sisters were Catherine, Queen of England, Queen Joanna I of Castile, and Maria, Queen of Portugal. Constance of Burgundy (8 May 1046 – 1093) was the daughter of Duke Robert I of Burgundy and Helie de Semur-en-Brionnais.  She was Queen consort of Castile and León by her marriage to Alfonso VI of León and Castile.  She was the granddaughter of King Robert II of France, the second monarch of the French Capetian dynasty.  She was the mother of Urraca of León, who succeeded her father in both Castile and León. The Kingdom of New Spain was established following the Spanish conquest of the Aztec Empire in 1521 as a New World kingdom dependent the crown of Castile, since the initial funds for exploration came from Queen Isabella of Castile.  Although New Spain was a dependency of Castile, it was a kingdom itself not a colony, but subject to the monarch of Castile.  The monarch had sweeping power in the overseas territories, The king possessed not only the sovereign right but the property rights; he was the absolute proprietor, the sole political head of his American dominions.  Every privilege and position, economic political, or religious came from him.  It was on this basis that the conquest, occupation, and government of the [Spanish] New World was achieved. Álvaro Núñez de Lara ( 1170 – 1218) was a Castilian nobleman who played a key role, along with other members of the House of Lara, in the political and military affairs of the Kingdoms of León and Castile around the turn of the 13th century.  He was made a count in 1214, served as "alférez" to King Alfonso VIII of Castile, was the regent during the minority of King Henry I of Castile, and was "mayordomo" (steward) to King Alfonso IX of León.  He opposed Queen Berengaria of Castile and her son King Ferdinand III and supported the King of León during the war between the two countries of 1217–1218.  At the end of his life he was a knight of the Order of Santiago, in whose Monastery of Uclés he was buried. Joanna (6 November 1479 – 12 April 1555), called the Mad (Spanish: "Juana la Loca" ), was queen of Castile from 1504 and of Aragon from 1516.  From the union of these two crowns modern Spain evolved.  Joanna married Philip the Handsome on 20 October 1496.  Philip was crowned King of Castile in 1506, initiating the rule of the Habsburgs in Spain.  After Philip's death that same year, Joanna was deemed mentally ill and was confined to a nunnery for the rest of her life.  Though she remained the legal queen of Castile throughout this time, her father, Ferdinand II of Aragon, was regent until his death, when she inherited his kingdom as well.  From 1516, her son, Charles I, ruled as king, while she nominally remained co-monarch. Guillén Pérez de Guzmán (ca.  1180 –1233), a member of the House of Guzmán, one of the most aristocratic of the Kingdom of Castile, was the maternal grandfather of Queen Beatrice of Castile, Queen Consort of Portugal as the wife of King Alfonso III.  His father was Pedro Rodríguez de Guzmán—killed in the Battle of Alarcos on July 18, 1195 and son of Rodrigo Muñoz de Guzmán—and Mahalda With his brothers Nuño and Theobald, he fought alongside King Alfonso VIII at the decisive Battle of Navas de Tolosa in 1212.  Even though his kinsmen supported the Laras during the crisis that ensued after the death of King Alfonso VIII, Guillén, probably because of his marriage to a member of the Girón clan, supported Queen Berengaria of Castile and her son, the future king Ferdinand III. Henry I of Castile (14 April 1204 – 6 June 1217) was king of Castile.  He was the son of Alfonso VIII of Castile and Eleanor of England, Queen of Castile (daughter of Henry II of England and Eleanor of Aquitaine).
Answer: Holy Roman Emperor Maximilian I