Frederick Charles of Schleswig-Holstein-Sonderburg-Plön (4 August 1706, in Sønderborg – 18–19 October 1761, in Traventhal), known as Friedrich Karl or Friedrik Carl of Holstein-Plön, was a member of a cadet branch of the Danish royal family and the last duke of the Duchy of Schleswig-Holstein-Sonderburg-Plön (or Holstein-Plön), a Danish royal prince, and a knight of the Order of the Elephant.

When he died without a male heir born of his marriage to Countess Christine Armgard von Reventlow, rule of the Duchy of Holstein-Plön returned to the Danish crown.

Frederick Charles's accession was delayed until 1729 because his father had contracted a morganatic marriage with his mother, Dorothea Christina von Aichelberg, who was recognised as a Danish princess by the King only years after her husband's death.

Frederick Charles had six children from his marriage with Countess Christine Armgard von Reventlow (1711–1779), a daughter of the Danish general Christian Detlev, Count von Reventlow, and niece of the Danish queen consort Anne Sophie von Reventlow, who, as had his mother, had been born into a non-dynastic noble family:[2] Additionally, Frederick Charles had children by two mistresses: by Sophie Agnes Olearius, with whom he conducted a six-year liaison, six daughters; and by his maîtresse-en-titre, Maria Catharina Bein, sister of the court chamberlain, three sons (two of whom died childless) and two daughters (one of whom died in childhood), all of whom the duke recognized and legitimated, and on whom (or their mothers) he bestowed lands, titles, and money.

[3] On the 30 January 2024 episode of Finding Your Roots, it was shown that Frederick Charles is a sixth-great-grandfather of American actor Bob Odenkirk, through his mistress Maria Catharina Bein and his last surviving son, Friedrich Carl Steinholz.