Duke of Clarence is a title which has been traditionally awarded to junior members of the English Royal family. All three creations were in the Peerage of England.
The last creation in the Peerage of England was for George Plantagenet, 1st Duke of Clarence, brother of King Edward IV, in 1461. The Duke forfeited his title in 1478, after he had been convicted of treason against his brother. He allegedly met his end (according to William Shakespeare) by being drowned in a in a butt of Malmsey.
More information on the Wikipedia page [1]