Philipp joined the Nazi Party in 1930, and, when they gained power with the appointment of Adolf Hitler as Chancellor in 1933, he became Oberpräsident of the Prussian Province of Hesse-Nassau.

[4] Philipp was born at Schloss Rumpenheim in Offenbach, the third son of Prince Frederick Charles of Hesse and of his wife Princess Margaret of Prussia (sister of the German Emperor Wilhelm II).

It was intended that Philipp would eventually succeed his father as Head of the House of Hesse, while his (younger) twin brother Wolfgang would be heir to the Finnish throne.

Following the war, Philipp was a member of the Übergangsheer (the Transitional Army, precursor to the Reichswehr) which was successful in repressing communist and socialist action.

[5][6] He married Princess Mafalda of Savoy, daughter of King Victor Emmanuel III of Italy, on 23 September 1925 at the Castello di Racconigi near Turin.

Through his party membership, Philipp became a particularly close friend of Hermann Göring, the future head of the German Air Force (Luftwaffe).

He introduced other aristocrats to NSDAP officials and, as son-in-law of the king of Italy, was a frequent go-between for Hitler and Benito Mussolini.

For this purpose, the Reich Chancellery established a special account for him at the German Embassy in Rome, over which Prince Philipp could freely dispose.

In February 1941, Philipp signed the contract placing the sanitarium of Hadamar Clinic at the disposal of the Reich Interior Ministry.

As the war progressed, the attitude of the National Socialist authorities towards members of the German princely houses changed.

In May 1943, Hitler issued the "Decree Concerning Internationally Connected Men" declaring that princes could not hold positions in the party, state, or armed forces.

The arrest of Mussolini by Philipp's father-in-law King Victor Emmanuel in July 1943 made Phillip's position even more difficult.

[2] Philipp was held by the Allies in Naples and subsequently was transferred to Camp Ashcan in Luxembourg and then to a series of other detention centres until 1947.

Subsequent appeals concluded in February 1949, and resulted in a reclassification as Category IV (follower) and a reduction of his fine to 36,568 DM.

Louis had nominally adopted Philipp's son Moritz, who at that time inherited the Hessian and by-Rhine properties, including remarkable cultural collections: for the first time since the division of Hesse into branches after the death of Philip the Magnanimous in 1567, all sovereign branches of the house of Hesse were reunited again.