Question: Who was the king of Spain during Ferdinand III's second year as Holy Roman Emperor?

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List of Holy Roman Empresses: Holy Roman Empress or Empress of the Holy Roman Empire is the title given to the consort (wife) or regent of the Holy Roman Emperor.  The elective dignity of Holy Roman Emperor was restricted to males only, therefore there was never a Holy Roman Empress regnant, though women such as Theophanu or Maria Theresa of Austria, who controlled the power of rule, served as de facto Empresses regnant.

Maria Leopoldine of Austria: Maria Leopoldine of Austria-Tyrol (6 April 1632 – 7 July 1649), was by birth Archduchess of Austria and member of the Tyrolese branch of the House of Habsburg and by marriage the second spouse of her first cousin, Holy Roman Emperor Ferdinand III.  As such, she was Empress of the Holy Roman Empire, German Queen and Queen consort of Hungary and Bohemia.  She died in childbirth.

Giovanni Battista Buonamente: Giovanni Battista Buonamente (ca. 1595 – 1642) was an Italian composer and violinist in the early Baroque era.  He served the Gonzagas in Mantua until about 1622, and from about 1626 to 1630 served the Holy Roman Emperor Ferdinand II, Holy Roman Emperor in Vienna.  Notably, in 1627 he played for the coronation festivities in Prague of Ferdinand III, son of the emperor.  He then served as the violinist of Madonna della Steccata church in Parma.  After a short service there, he arrived at his final position in 1633 of "maestro di cappella" at Assisi.

Dukedom of Amalfi: The Duke of Amalfi is a Spanish ducal title first created in 1639 by King Philip IV for Prince Ottavio Piccolomini, a Holy Roman Imperial Army Field Marshal.

Wolfgang Ebner: Wolfgang Ebner (16121665) was a German baroque composer.  He was a Viennese court organist in the latter years of the reign of Ferdinand III, Holy Roman Emperor, and then of Leopold I, Holy Roman Emperor.

Leopold I, Holy Roman Emperor: Leopold I (name in full: "Leopold Ignaz Joseph Balthasar Felician"; Hungarian: "I. Lipót" ; 9 June 1640 – 5 May 1705) was Holy Roman Emperor, King of Hungary, Croatia, and Bohemia.  The second son of Ferdinand III, Holy Roman Emperor, by his first wife, Maria Anna of Spain, Leopold became heir apparent in 1654 by the death of his elder brother Ferdinand IV.  Elected in 1658, Leopold ruled the Holy Roman Empire until his death in 1705.

Maria Anna of Spain: Maria Anna of Spain (18 August 1606 – 13 May 1646), was by birth Infanta of Spain and by marriage Holy Roman Empress and Queen of Hungary and Bohemia as the wife of Ferdinand III, Holy Roman Emperor.

Otto Heinrich Fugger, Count of Kirchberg: Otto Heinrich Fugger, Count of Kirchberg and Weissenhorn (1592–1644) was promoted to be a Knight of the Order of the Golden Fleece in 1628.  He was the son of Christoph Fugger von Glött, deceased 1615, the grandson of Johann Fugger, deceased 1598, the great grandson of very wealthy Augsburg city International businessman and banker Anton Fugger (1493–1560).  The 16th century Fugger's, descendents of a German businessmen family tracked down to the 14th century, were the Imperial bankers with King Charles I of Imperial Spain, also Holy Roman Emperor as Charles V (1500–1558), and his brother, also Holy Roman Emperor, Ferdinand I of Habsburg (1503–1564), king of Hungary and Bohemia from 1526, emperor from 1556 by abdication of his brother Charles.

Ferdinand III, Holy Roman Emperor: Ferdinand III (13 July 1608 – 2 April 1657) was Holy Roman Emperor from 15 February 1637 until his death, as well as King of Hungary and Croatia, King of Bohemia and Archduke of Austria.  He was the last emperor to have real power over the Holy Roman Empire.

List of monarchs of Prussia: The monarchs of Prussia were members of the House of Hohenzollern who were the hereditary rulers of the former German state of Prussia from its founding in 1525 as the Duchy of Prussia.  The Duchy had evolved out of the Teutonic Order, a Roman Catholic crusader state and theocracy located along the eastern coast of the Baltic Sea.  The Teutonic Knights were under the leadership of a Grand Master, the last of whom, Albert, converted to Protestantism and secularized the lands, which then became the Duchy of Prussia.  The Duchy was initially a vassal of the Kingdom of Poland, as a result of the terms of the Prussian Homage whereby Albert was granted the Duchy as part of the terms of peace following the Prussian War.  When the main line of Prussian Hohenzollerns died out in 1618, the Duchy passed to a different branch of the family, who also reigned as Electors of Brandenburg in the Holy Roman Empire.  While still nominally two different territories, Prussia under the suzerainty of Poland and Brandenburg under the suzerainty of the Holy Roman Empire, the two states are known together historiographically as Brandenburg-Prussia.  Following the Second Northern War, a series of treaties freed the Duchy of Prussia from any vassalage to any other state, making it a fully sovereign Duchy in its own right.  This complex situation (where the Hohenzollern ruler of the independent Duchy of Prussia was also a subject of the Holy Roman Emperor as Elector of Brandenburg) laid the eventual groundwork for the establishment of the Kingdom of Prussia in 1701.  For diplomatic reasons, the rulers of the state were known as the King in Prussia from 1701 to 1772; largely because they still owed fealty to the Emperor as Electors of Brandenburg, the "King in Prussia" title (as opposed to "King of Prussia") avoided offending the Emperor.  As the Prussian state grew through several wars and diplomatic moves throughout the 18th century, it became apparent that Prussia had become a Great Power that did not need to submit meekly to the Holy Roman Empire.  By 1772, the pretense was dropped, and the style "King of Prussia" was adopted.  Thus it remained until 1871, when in the aftermath of the Franco-Prussian War, the King of Prussia Wilhelm I was crowned German Emperor.  From that point forward, though the Kingdom of Prussia retained its status as a constituent state of the German Empire, all remaining Kings of Prussia also served as German Emperor, and that title took precedence.

Supporting paragraphs: Dukedom of Amalfi Ferdinand III, Holy Roman Emperor
Answer: King Philip IV