Post monarchy In May 1931 against the will of his father,  Friedrich Franz joined the SS and by 1936 he had been promoted to the rank of Hauptsturmführer (Captain).  He was posted to Denmark during World War II where he worked at the German embassy as a personal aide to Werner Best. 
Frederick Francis IV (Friedrich Franz Michael; 9 April 1882 – 17 November 1945) was the last Grand Duke of Mecklenburg-Schwerin and regent of Mecklenburg-Strelitz. He inherited the throne when he was fifteen years old in 1897 and was forced to renounce it in 1918. Early life
Friedrich Franz, Hereditary Grand Duke of Mecklenburg-Schwerin in Biographical Summaries of Notable People Friedrich Franz Michael Wilhelm Nikolaus Franz-joseph Ernst August Hans Von Mecklenburg-Schwerin in MyHeritage family trees (Hussey Web Site)
Biography He was born in Schloss Ludwigslust, the eldest son of Hereditary Grand Duke Paul Friedrich of Mecklenburg-Schwerin and his wife Princess Alexandrine of Prussia. He became heir apparent to the grand duchy following the death of his great-grandfather Frederick Francis I on 1 February 1837.
Frederick Francis III ( German: Friedrich Franz Paul Nikolaus Ernst Heinrich; 19 March 1851 – 10 April 1897) was the penultimate Grand Duke of Mecklenburg-Schwerin . Biography He was born in Schloss Ludwigslust as the son of Frederick Francis II, Grand Duke of Mecklenburg-Schwerin and his first wife Princess Augusta Reuss of Köstritz.
Frederick Francis I (10 December 1756 – 1 February 1837) ruled over the German state of Mecklenburg-Schwerin, first as duke (1785–1815), and then as grand duke (1815–1837). Biography Fredrick Francis I, in uniform, wearing the Star and Sasch of the Prussian Order of the Black Eagle and the Order of the Red Eagle around the neck.
Genealogy for Friedrich Franz III Paul Nikolaus Ernst Heinrich von Mecklenburg (Mecklenburg-Schwerin), Großherzog zu Mecklenburg-Schwerin (1851 - 1897) family tree on Geni, with over 250 million profiles of ancestors and living relatives.
In May 1943, a family council was called by the Grand Ducal family and Friedrich Franz was passed over as heir in favour of his younger brother Duke Christian Louis, who would instead inherit the family property.
Summarize this article for a 10 years old. Frederick Francis I (10 December 1756 – 1 February 1837) ruled over the German state of Mecklenburg-Schwerin, first as duke (1785–1815), and then as grand duke (1815–1837).