The Catholic Monarchs and the House of Austria
The Catholic Kings flew a flag that combined the coat of arms of Aragon with those of Castile and those of León. This proto-flag was also used by Felipe el Hermoso, husband of their daughter, Juana la Loca, who brought the Burgundy cross with him.
His son, Carlos I of Spain and emperor of the Holy Roman Empire, took the Burgundy cross as a personal emblem and thus became widespread among the different Spanish kingdoms.
Although the red cross with the white background is always used to remember the Hispanic Empire, the reality is that this was not the symbol of the Spanish states, but the monarch’s staff.
In fact, not even of all the monarchs of the Austrian or Habsburg house, since Philip II changed his colors: he kept the red cross, but the background preferred it yellow.
Cross of Burgundy or Cross of San Andrés, which, with very different designs, was used by the navy who always wore the emblem, since the design became the most varied in colors and shapes according to the regiment.