Charles II was the final Habsburg ruler of the Spanish Empire. Crowned just before his fourth birthday in late 1665, his rule, such as it was, died with him in 1700 at age 38.
Charles was the only son of Philip IV and his niece Mariana of Austria, and counted the famed Joanna the Mad as a recent ancestor. He had perhaps the most pronounced case of Habsburg lip ever known in royalty—his underbite was so severe, he could not make his upper and lower teeth meet. His tongue filled his mouth to the point that he could barely be understood when attempting to speak. One history book or another described his life as "a prolonged infancy that developed into a premature senility".
The king married twice: first to Marie Louise d'Orléans in 1679, who died ten years later, then to Maria Anna of Neuburg. Attempts to produce an heir failed, so he named Philip of Anjou, Louis XIV's grandson, as his heir. This lead directly to the War of the Spanish Succession and to the end of the Habsburgs as a political force in Spain. During his 34-year rule, he left governance for the most part to his advisors. Given his reputed lack of hygiene and barriers to communication caused by his physiology, this was probably for the best.
A number of official portraits of Charles II were made during his lifetime. All of them try, but completely fail to downplay the jaw deformities and cranial enormity the king suffered from in life.
Somehow, this didn't have much of an effect on ending the practice of incestuous royal marriage, which remained very popular into the nineteenth century in mainland Europe and persists to this day in the United Kingdom, Norway and the Netherlands.
Brevity Quest 2019: 295 words.
https://madmonarchs.blogspot.com/2013/11/the-habsburg-kings-of-spain-descended.html
https://scienceblogs.com/notrocketscience/2009/04/14/how-inbreeding-killed-off-a-line-of-kings