John II of Oldenburg was Count of Oldenburg from 1275 until ca. 1301.

He was the son of Christian III, Count of Oldenburg and Hedwig von Oldenburg in Wildeshausen

Wildeshausen

Wildeshausen is a town and the capital of the Oldenburg district in Lower Saxony, Germany. It is situated by the river Hunte.-History:...

. John married twice, first to Elisabeth, the daughter of John, Duke of Brunswick and Lunenburg and Liutgard von Holstein-Itzehoe. His second marriage was to Countess Hedwig of Diepholz.

John had five children:

1. Christian IV, Count of Oldenburg
2. John III, Count of Oldenburg, married Mechtild (Matilda) of Bronckhorst
3. Conrad I, Count of Oldenburg
   Conrad I, Count of Oldenburg
   Conrad I of Oldenburg was Count of Oldenburg from 1344 to 1368.He was the son of John II of Oldenburg and Hedwig of Diepholz. Conrad married Ingeborg, the daughter of Count Gerard IV of Holstein-Plön. Four children were born of this union:#Conrad II, Count of Oldenburg Conrad I of Oldenburg...
   
   
4. Maurice of Oldenburg (killed in action in 1368 near Blexen
   Nordenham
   Nordenham is a town in the Wesermarsch district, in Lower Saxony, Germany. It is located at the mouth of the Weser river on the Butjadingen peninsula on the coast of the North Sea. The seaport city of Bremerhaven is located on the other side of the river...
   
   ), Dean (Domdechant)
   Dean (religion)
   A dean, in a church context, is a cleric holding certain positions of authority within a religious hierarchy. The title is used mainly in the Anglican Communion and the Roman Catholic Church.-Anglican Communion:...
   
    of Bremen Cathedral
   Bremen Cathedral
   Bremen Cathedral , dedicated to St. Peter, is a church situated in the market square in the center of Bremen, in northern Germany. The cathedral belongs to the Bremian Evangelical Church, a member of the Protestant umbrella organisation named Evangelical Church in Germany...
   
   , Diocesan Administrator of the Archdiocese of Bremen (1345–1362), Archbishop Elect of Bremen (1348, papally refused) and coadjutor of Bremen (1348–1360)
5. Gisela of Oldenburg, married Gerhard III, Count of Hoya

John II of Oldenburg is also the male-line ancestor of Queen Margrethe II of Denmark

Margrethe II of Denmark

Margrethe II is the Queen regnant of the Kingdom of Denmark. In 1972 she became the first female monarch of Denmark since Margaret I, ruler of the Scandinavian countries in 1375-1412 during the Kalmar Union.-Early life:...

, Philip, Duke of Edinburgh, and thus of Charles, Prince of Wales

Charles, Prince of Wales

Prince Charles, Prince of Wales is the heir apparent and eldest son of Queen Elizabeth II and Prince Philip, Duke of Edinburgh. Since 1958 his major title has been His Royal Highness The Prince of Wales. In Scotland he is additionally known as The Duke of Rothesay...

 and Prince William, Duke of Cambridge.