Olaf I of Norway and Martha of Sweden were first cousins (not so modern-day but, you get the point).
That was Olav V. The first King Olav of Norway was the Viking king Olav Tryggvason (960s – 1000), who grew up in Russia. Yes, Anglophone Romanov fans are usually too culturally saturated with the Stuarts and other stuff in the Anglo-Celtic mists to be curious about anything concerning that huge part of Russian history which centers on the Baltic and includes the Nordic countries, a theme most poignantly crowned in NAOTMAA's Finnish holidays.
(Not that Olav Tryggvason was without links to the Celtic mists, this first Norwegian crusader/missionary king was baptized by a hermit in the Scilly Isles, but it's fascinating to speculate whether he had already been exposed to Christianity in Russia, especially in the service of Vladimir Sviatoslavich the Great, the first Christian Grand Prince of Kiev, whom he served after having lived his first years in Russia as a slave, having been captured by Estonian pirates on his way over the Baltic as an exiled Norwegian pretender.)
