I thought they meant when the King of England was an actual frenchman and French was the upper-class language of the UK.
They are all related. From Niall Ferguson's- The Square and the Tower "The Times noted in 1863, the history of the Saxe-Coburgs showed ‘how much one success leads to another in Princely life’. Augusta of Saxe-Coburg’s grandchildren included not only both Queen Victoria and her husband, Albert, but also Ferdinand, who married the Queen of Portugal, and Leopold’s son, namesake and heir to the Belgian throne. The Saxe-C…
(Norway #73, Yugoslavia #103, Sweden #283, Denmark #321, Greece #565, Spain #699, The Netherlands #1160, Belgium #1345, Luxembourg #1687, Liechtenstein #1916, Romania #4146, etc... There's even a Napoleon in there. And a million German princes.)