[1] His father, the then hereditary prince (who reigned from 1760 and died in 1785) had in 1747 left the family and soon converted to Catholicism, and in 1755 formally ended his marriage.

The young prince Frederick, together with his two elder brothers, were with their mother the Landgravine Mary and became fostered by Protestant relatives in 1747.

Soon the family moved to Denmark to be guests of her sister Louise of Great Britain, who died in 1751.

In 1815, the prince was in command of the Royal Danish Auxiliary Corps mobilized as part of the Seventh Coalition against Napoleonic France.

1781 he bought Rumpenheim Castle, Offenbach, from his brother Carl, and it became the family's seat.