1832: King Leopold I of the Belgians married Princess Louise of Orléans, eldest daughter of King Louis-Philippe of the French
1840: Queen Louise's brother, Prince Louis of Orléans, Duke of Nemours (second son of King Louis-Philippe of the French), married Princess Victoria of Saxe-Coburg and Gotha (Koháry branch), a niece of King Leopold I of the Belgians
1843: Victoria's brother, Prince August of Saxe-Coburg and Gotha (Koháry branch), married Louis' sister, Princess Clémentine of Orléans
1896: Louis and Victoria's grandson, Prince Emmanuel of Orléans, Duke of Vendôme (son of Prince Ferdinand of Orléans, Duke of Alençon and Duchess Sophie Charlotte in Bavaria), married Princess Henriette of Belgium, granddaughter of King Leopold I and Queen Louise. The two were second cousins, once removed.
Have I gotten them all? Are there additional examples?