Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her first son, Prince Wilhelm (1906 - 1940), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her first son, Prince Wilhelm (1906 - 1940), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Crown Prince Friedrich Wilhelm of Germany and Prussia (1882 - 1951), with his wife Cecilie of Mecklenburg-Schwerin (1886 - 1954) and their sons, Princes Wilhelm (1906 - 1940), Louis Ferdinand (1907 - 1994), Hubertus (1909 - 1950) and Friedrich (1911 - 1966), circa 1915. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Crown Prince Friedrich Wilhelm of Germany and Prussia (1882 - 1951), with his wife Cecilie of Mecklenburg-Schwerin (1886 - 1954) and their sons, Princes Wilhelm (1906 - 1940), Louis Ferdinand (1907 - 1994), Hubertus (1909 - 1950) and Friedrich (1911 - 1966), circa 1915.  (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her sons, Prince Louis Ferdinand (1907 - 1994, front) and Prince Wilhelm (1906 - 1940), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her sons, Prince Louis Ferdinand (1907 - 1994, front) and Prince Wilhelm (1906 - 1940), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her second son, Prince Louis Ferdinand (1907 - 1994), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Cecilie of Mecklenburg-Schwerin, Crown Princess of Germany and Prussia (1886 - 1954) with her second son, Prince Louis Ferdinand (1907 - 1994), 1908. (Photo by Estate of Emil Bieber/Klaus Niermann/Getty Images)

Prince William of Hohenzollern (1882-1951) aka Crown Prince, son of kaiser WilliamII, here with his wife Cecilie of Mecklenburg-Schwerin c. 1925. (Photo by APIC/Getty Images)

Prince William of Hohenzollern (1882-1951) aka Crown Prince, son of kaiser WilliamII, here with his wife Cecilie of Mecklenburg-Schwerin c. 1925. (Photo by APIC/Getty Images)