Queen Juliana of the Netherlands (1909-2004) was the paternal first cousin of Queen Alexandrine of Denmark (1879-1952) and crown princess Cecilie of Germany (1886-1954) who were of the same age as her father their uncle Heinrich (1876-1934).
Alexandrine's daughter-in-law Ingrid of Sweden was the sister and first cousin of several princes who were considered as potential spouses for Juliana.
Alexandrine's younger son Knud never was, probably because of the family relation with Juliana.
I know that in a large family with children spaced apart in years, you can have large gaps in age between the oldest and the youngest. The result can be young aunts and uncles, or even people born already aunts and uncles (meaning that they have nieces or nephews older than themselves). Other interesting family scenarios are possible, when you add marriage into the equation, meaning in-laws.
For instance, Russia's last empress, born Princess Alix of Hesse-Darmstadt, had a much older sister (Elisabeth) who was married to the Grand Duke Sergei Alexandrovich -- uncle of Czar Nicholas II. So the result was that you had a pair of sisters where the older one was an aunt by marriage, as well as a sister-in-law, to the husband of the younger one.
Princess Alexandra of Greece and Denmark (eldest daughter of King George I and his queen consort, born Grand Duchess Olga Constantinovna of Russia), married her first cousin, once removed, the Grand Duke Paul Alexandrovich of Russia. Although she was technically a second cousin to Queen Marie of Romania (a granddaughter of Queen Victoria of Great Britain and Czar Alexander II of Russia), meaning a member of the same generation (and who wasn't that much older than herself) she was referred to in the latter's memoirs as "aunt", since that's what she was by marriage.
And Queen Louise of Sweden, consort of King Gustaf VI Adolf, became a stepmother to his five children, who were by blood her second cousins.
The list of "bizarre" family scenarios would undoubtedly be legion, especially if one were to include step relations into the picture. That being said, I'd be interested if anybody could provide me with relatively recent examples in European royal history of such occurrences.
Of course, it's difficult to qualify these things, since it's not easy to define *bizarre*. We have seen how Queen Mary of Great Britain, consort of King George V, was a second cousin of her father-in-law, King Edward VII. Similarly, Queen Anne of Romania was a second cousin of her mother-in-law, Queen Helen. But these situations are nothing compared to having older nieces and nephews.
Still, it's interesting to consider situations where a relative belonged to two generations from one's standpoint, depending on the connection. What are other examples?