Complex sentence: Nicholas and Alix had first met in 1884 at the wedding of Nicholas's Uncle Grand Duke Sergei to Alix's sister, Elizabeth, in St. Petersburg and when Alix returned to Russia in 1889 they fell in love.
Split into simpler sentences: Nicholas and Alix had first met in 1884 at the wedding of Nicholas's Uncle Grand Duke Sergei to Alix's sister, Elizabeth, in St. Petersburg. When Alix returned to Russia in 1889 they fell in love.