Due to the brilliant marital alliances of his children, he became known as the "Father-in-law of Europe." Dagmar's eldest brother would succeed his father as King Frederick VIII of Denmark (one of whose sons would be elected as King of Norway). Her elder, and favourite, sister, Alexandra married Albert Edward, the Prince of Wales (the future King Edward VII) in March 1863. Alexandra, along with being queen consort of King Edward VII, was also mother of George V of the United Kingdom, which helps to explain the striking resemblance between their sons Nicholas II and George V. Within months of Alexandra's marriage, Dagmar's second older brother, Wilhelm, was elected as King George I of the Hellenes. Her younger sister was Thyra, Duchess of Cumberland. She also had another younger brother, Valdemar.