Prince Frederick of Prussia (1911–1966)

On 30 July 1945, he married Lady Brigid Guinness, daughter of Rupert Guinness, 2nd Earl of Iveagh, at Little Hadham, Hertfordshire and they had five children:[2]

• Frederick Nicholas (born 3 May 1946) married to Hon. Victoria Lucinda Mancroft, four children;
• Andreas (born 14 November 1947) married to Alexandra Blahova, two children;
• Victoria Marina (born 22 February 1952) married to Philippe Alphonse Achache, issue;
• Rupert (born 28 April 1955) married to Ziba Rastegar-Javaheri, two children;
• Antonia (born 28 April 1955) married to Charles Wellesley, 9th Duke of Wellington, issue.

He was studying at Cambridge, living incognito as the Count von Lingen, when war broke out in September 1939. He was arrested and interned in May 1940. He was held in Britain for several months, then sent to internment camps near Quebec City and soon afterwards, Farnham, Quebec. In both camps, he was elected camp leader by fellow inmates.[3]

He renounced his German citizenship in 1947.[2] He was naturalised as a British citizen in October 1947 under the name Friedrich von Preussen (having also been known during residence in the UK as "George Mansfield").[2] This naturalization was controversial, in part because being a descendant of Sophia of Hanover, and having rights under the Act of Settlement 1701, as amended by the Sophia Naturalisation Act 1705, he had a claim to British citizenship from birth. His status in context of his claim for compensation for property seized in Poland was debated in Parliament and the law courts until 1961.[1]

He was the owner of Reinhartshausen Castle at Erbach, Germany. While staying there in 1966, he went missing and was found two weeks later, having drowned in the Rhine, whether suicidally or accidentally could not be determined.[2]