Philipp Friedrich Alexander, Prince of Eulenburg and Hertefeld, Count of Sandels (German: Philipp Friedrich Alexander Fürst zu Eulenburg und Hertefeld Graf von Sandels; 12 February 1847 – 17 September 1921) was a diplomat and composer of Imperial Germany who achieved considerable influence as the closest friend of Wilhelm II.
He was the central member of the so-called Liebenberg Circle, a group of artistically minded German aristocrats within Wilhelm's entourage.
Eulenburg played an important role in the rise of Bernhard von Bülow, but fell from power in 1907 due to the Harden–Eulenburg affair when he was accused of homosexuality.