Dieter Stanzeleit, 71, says he has copies of Romanian intelligence documents, from 1939, 1951 and 1978 that attest to Michael marrying a British woman, and to his existence. Romania's royal family opposes his claim. The 89-year-old former king will be called to a court in April to take the test.
Michael ruled Romania from 1927 to 1930, and from 1940 until 1947. Mr Stanzeleit was adopted by a German family after the Second World War.