These are examples from Swedish history:
The Wasa dynasty (1523-1654): King Gustav I, who we usually call Gustav Wasa, was married three times. His first wife and queen was Katarina of Sachsen-Lauenburg. She gave birth to a son, the future king Erik XIV, but she died soon after that. The king soon re-married, and Margareta Leijonhufwud became his second wife and queen. She gave birth to many children, including the future kings Johan III and Carl IX. She was never pleased with the fact, that her step-son Erik was close to the throne than her own sons. Queen Margareta died, and the aging King Gustav married a third time, to seventeen-year-old Katarina Stenbock. Katarina Stenbock had no children, and she was only twentyfive years old, when she became a widow at the king's death eight years later. When King Gustav died, Crown prince Erik became King Erik XIV. But he didn't get along well with his half-brothers Johan and Carl. Soon enough, they overthrew their brother, and Johan became King Johan III, and Erik's children never inherited the Swedish thrown. After Johan's death, his son Sigismund became king. But he was a Catholic, since his mother was the Polish princess Catherine Jagellonica, and he also was the king of Poland after his grandfather. Gustav Wasa had turned Sweden into a Lutheran country, and Catholics were suspicious at the time. Finally, Sweden was taken away from him, and his uncle Carl became King Carl IX, so Sigismund had to do with Poland. After Carl IX:s death, his son Gustav II Adolf and his granddaughter Christina were the last two Swedish monarchs of the Wasa dynasty. At least two unexpected kings there.
The Pfalz dynasty (1654-1751): After Queen Christina (the woman in my avatar and my namesake) abdicated and became Catholic, her cousin Carl Gustav became king Carl X Gustav. His son was King Carl XI and his grandson was KIng Carl XII. No problems there, except for that both Carl X Gustav and Carl XI died before their sons were adults. But then, Carl XII didn't want to marry. He was only abroad waring, and no children were born. When King Carl XII eventually died in the war without issues, his sister Ulrika Eleonora became quéen. Two years later, she gave the thrown to her husband Frederic of Hessen-Kassel, and they were co-regents for years. These two were unexpected monarchs.
The Holstein-Gottorp dynasty (1751-1818): However, Ulrika Eleonora never had children, and Frederic's children with his mistress Hedvig Taube had no right to inherit the thrown. Instead, he adopted Prince Adolf Frederic of Holstein-Gottorp. He later became king of Sweden, even though he never learned to speak Swedish, and is most known for eating himself to death on wheat buns (even if his meal also consisted of other food). His son became King Gustav III, a much more famous historical figure. But Gustaf III didn't have luck with his marriage to Sophie Madeleine of Denmark, and it took a long time for them to get children. When King Gustav died after he had been shot at a theater (he loved theaters and everything cultural), his son Gustav Adolf was only fourteen years old. However, the boy became King Gustav IV Adolf. When he lost Finland to Russia in a war, he had to abdicate and flee the country with his family. His elderly uncle Carl, Gustaf III:s younger brother, became king Carl XIII. One unexpected king there.
The Bernadotte dynasty (1818 - present): But like Frederic of Hessen-Kassel, Carl XIII had illegimate children, but no children by his wife. He had to adopt, and after the first choice, a Danish prince, had died, the choice fell on French general Jean Baptiste Bernadotte. He was a good warrior in the critical times of the Napoleon wars, and he had a young son, Oscar, whose mere existence was a good security for the survival of the royal house. Soon enough, Jean Baptise Bernadotte became King Carl XIV Johan. In due time, his son Oscar became King Oscar I and his grandson Carl became King Carl XV. But Carl and his wife Louise of the Netherlands didn't have it easy. They had a daughter and a son. But little Prince Carl died, and Princess Louise was now their only child. But Louise had two uncles, Oscar and August, and her uncle Oscar kept getting sons with his wife Sophie of Nassau. Surrounded by all these male relatives, Louise couldn't be heir, and instead, she was married off to Denmark, where she became the wife of the future King Frederic VIII. She eventually became Queen Louise of Denmark and the mother King Christian X of Denmark and King Haakon VIII of Norway. But Sweden was lost for her, and when her father King Carl XV died, his brother Oscar became Oscar II. That's an unexpected monarch. Oscar II was the father of King Gustav V, who was the father of King Gustav VI Adolf. But since Gustav VI Adolf's son Gustav Adolf Edmund died in a plane crash, his grandson had to succeed him as King Carl XVI Gustaf. That's the only example of skipping a generation in Swedish history.
