I believe that you are referring to Nicholas II, who wanted Olga to marry Carol of Romania.
Nicholas I married his daughter Olga off to king Karl I of Württemberg, after the 'insignificant' marriage of her elder sister Maria to Maximilian de Beauharnais, 3rd duke of Leuchtenberg, grandson of Max I of Bavaria and of Empress Josephine of France.
It seems that Olga met Max (II) while she was visiting Prussia in 1838. The Bavarian RF wanted Max to marry a Russian GDss. They thought of Maria, but he was attracted by Olga as he she resembled one of the portraits in a Bavarian palace. Olga refused to think about the marriage, netiher she nor her family liked him. Other candidates were STephan of Austria, Friedrich-Wilhelm of Hesse-Kassel (who fell in love with the younger sister, Alexandra), duke Adolf of Nassau (who fell in love with Olga's cousing GDss Elisabeth) Finally they settled for Crown Prince Charles of Württemberg, the couple first met in Palermo.