E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Duke or Darling.
Heads or tails; pitch and toss. When the scandals about the Duke of York and Mrs. Clarke were the common talk of the town, the street boys, instead of crying Heads or tails, used to say Duke or Darling. (Lord Colchester: Diary, 1861.)