His parents were Janusz Franciszek, Prince Radziwiłł (1880–1967) and his wife, Princess Anna Lubomirska (1882–1947).

Radziwiłł married Rose de Mauléon (1913–1996), on 10 April 1940,[1] former niece-in-law of Irina Ovtchinnikova, wife of Prince Peter of Greece and Denmark.

The marriage produced one son: Grace Maria Kolin later married William Ward, 3rd Earl of Dudley (1894–1969) as his third wife, and from 1975, she lived with Robert B.

They had two children: Radziwiłł was one of the organisers of the Sikorski Historical Institute in London and founder of St. Anne's Church at Fawley Court, the site of Divine Mercy College, a school for boys of Polish origin, set up by the Marian Fathers in 1953 near Henley-on-Thames, England.

[2] The Radziwiłł family held the title Prince of the Holy Roman Empire since the early 16th century.