Diarmuid Ua Duibhne (Irish pronunciation: ) or Diarmid O'Dyna (also known as Diarmuid of the Love Spot), was the son of Donn and one of the Fianna in the Fenian Cycle of Irish mythology (traditionally set in the 2nd to 4th century). He is best known as the lover of Gráinne, the intended wife of Fianna leader Fionn mac Cumhaill in the legend The Pursuit of Diarmuid and Gráinne.