"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-Coburgs were further linked by marriage to the Orléans family and the Habsburgs. Moreover, Victoria and Albert’s eldest child was not the only one to marry royally: all but one of their nine children did. Thus, besides Frederick William of Prussia, Queen Victoria’s sons-in-law included Prince Christian of Schleswig-Holstein and Henry of Battenberg, whose brother Alexander became prince of Bulgaria, while her daughters-in-law included Princess Alexandra of Denmark and Princess Marie, daughter of Tsar Alexander II and sister of Tsar Alexander III. By the time the future Nicholas II arrived in London for his first visit to England, in 1893, a family reunion had come to resemble an international summit:
'We drew into Charing Cross. There we were met by: Uncle Bertie [the future Edward VII], Aunt Alix [Alexandra of Denmark], Georgie [the future George V], Louise, Victoria and Maud [his sisters, the last of whom would marry Prince Carl of Denmark, later Haakon VII of Norway] …
Two hours later Apapa [Christian IX of Denmark], Amama and Uncle Valdemar [of Denmark] arrived. It is wonderful to have so many of our family gathered together …
At 4.30 I went to see Aunt Marie [wife of Alfred, duke of Saxe-Coburg] at Clarence House and had tea in the garden with her, Uncle Alfred, and Ducky [their daughter, Victoria Melita].3
When this last married Ernest Louis, heir to the Grand Duchy of Hesse-Darmstadt the following year, the guests included an emperor and empress, a future emperor and empress, a queen, a future king and queen, seven princes, ten princesses, two dukes, two duchesses and a marquess. They were all related"
"In 1894, Queen Victoria was pleased to be addressed as ‘Granny’ by the future Tsar Nicholas II, after his betrothal to yet another of her granddaughters, Alix of Hesse.6 With ‘Willy’ (her grandson William II of Germany) corresponding cheerfully with his cousins ‘Nicky’ and ‘George’,7 it seemed for a time as if the vision that had inspired Leopold I had been realized: from Athens to Berlin, from Bucharest to Copenhagen, from Darmstadt to London, from Madrid to Oslo, from Stockholm to Sofia and even in St Petersburg, the Saxe-Coburgs ruled."
To say that it's the Saxe-Coburgs who rule all of Europe is... charitable. You could claim it's the other way around, after all, pretty much every single European monarch and royal house is somewhere in the British order of succession.
(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.)
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-Coburgs were further linked by marriage to the Orléans family and the Habsburgs. Moreover, Victoria and Albert’s eldest child was not the only one to marry royally: all but one of their nine children did. Thus, besides Frederick William of Prussia, Queen Victoria’s sons-in-law included Prince Christian of Schleswig-Holstein and Henry of Battenberg, whose brother Alexander became prince of Bulgaria, while her daughters-in-law included Princess Alexandra of Denmark and Princess Marie, daughter of Tsar Alexander II and sister of Tsar Alexander III. By the time the future Nicholas II arrived in London for his first visit to England, in 1893, a family reunion had come to resemble an international summit:
'We drew into Charing Cross. There we were met by: Uncle Bertie [the future Edward VII], Aunt Alix [Alexandra of Denmark], Georgie [the future George V], Louise, Victoria and Maud [his sisters, the last of whom would marry Prince Carl of Denmark, later Haakon VII of Norway] … Two hours later Apapa [Christian IX of Denmark], Amama and Uncle Valdemar [of Denmark] arrived. It is wonderful to have so many of our family gathered together … At 4.30 I went to see Aunt Marie [wife of Alfred, duke of Saxe-Coburg] at Clarence House and had tea in the garden with her, Uncle Alfred, and Ducky [their daughter, Victoria Melita].3
When this last married Ernest Louis, heir to the Grand Duchy of Hesse-Darmstadt the following year, the guests included an emperor and empress, a future emperor and empress, a queen, a future king and queen, seven princes, ten princesses, two dukes, two duchesses and a marquess. They were all related"
"In 1894, Queen Victoria was pleased to be addressed as ‘Granny’ by the future Tsar Nicholas II, after his betrothal to yet another of her granddaughters, Alix of Hesse.6 With ‘Willy’ (her grandson William II of Germany) corresponding cheerfully with his cousins ‘Nicky’ and ‘George’,7 it seemed for a time as if the vision that had inspired Leopold I had been realized: from Athens to Berlin, from Bucharest to Copenhagen, from Darmstadt to London, from Madrid to Oslo, from Stockholm to Sofia and even in St Petersburg, the Saxe-Coburgs ruled."