Christened Regina Helene Elisabeth Margarete, she was born in Würzburg, Germany, on January 6 1925, the youngest of four daughters of Prince Georg, the titular Duke Georg III of Saxe-Meiningen, and his wife, Countess Klara-Marie von Korff genannt Schmissing-Kerssenbrock. Her father, who had joined the Nazi party in 1933, died in a Russian prisoner-of-war camp at Chernopevetz a year after the war ended, when she was 21. Her sister died at only three months old, while one of her brothers, Prince Anton Ulrich, was killed in action at Albert-sur-Somme in 1940. Another became a Carthusian monk at Grande Chartreuse in Grenoble.

Further back, her great-grandfather was Georg II, Duke of Saxe-Meiningen (1826-1914), who after the Franco-Prussian War became a well-known patron of the theatre, and is sometimes described as having been the first modern stage director – he is remembered particularly for developing the Meiningen Ensemble, using his court theatre and designing costumes and props himself.

As a young girl, Regina studied social work at Bamberg, and later worked at a refugee home in Munich. In 1949 Archduke Otto von Habsburg came to visit some of his former Hungarian subjects who were being cared for at the home. The following year he and Regina became engaged.

Otto von Habsburg was barred from entering Austria until 1966, and owing to this injunction the couple were forced to marry elsewhere. The service eventually took place in France on May 10 1951 at the Eglise des Cordeliers in Nancy (the burial place of several members of the House of Lorraine), with the blessing of Pope Pius XII.

Although Otto was the heir to the Austrian Empire, he was unusual among "pretenders" in electing to ignore his aristocratic title, preferring to style himself Dr Otto von Habsburg; in 1979 he was voted into the European Parliament as Christian Democrat member for North Bavaria and served for the next 20 years, becoming the highly-regarded Father of the House and its only member to have been born before the First World War. He never claimed the throne of Austria, and in 2000 renounced his sovereignty of the Order of the Golden Fleece, the last sign of his leadership of the Imperial Family.

The Archduchess proved a devoted wife, and her husband acknowledged that, but for her support, he would not have been able to make such a success of his political career.

She herself was Protectress of the Order of the Starry Cross, an all-female Roman Catholic order founded in the 17th century; Grand Mistress of the Order of Elisabeth, a similar organisation; and an Honorary Lady Grand Cross of the Sovereign Order of Malta.

For some years she had suffered from heart problems, and in December 2005 had a stroke; but she recovered sufficiently to attend the wedding of a grandson in 2008.

The Archduchess died at Pöcking über Starnberg, Bavaria, at the villa where she had lived with her husband, who survives her, since 1953. They had two sons and five daughters. Their elder son, Karl, married Baroness Francesca Thyssen-Bornemisza, daughter of Baron Heini von Thyssen and his third wife, Fiona Campbell-Walter.