Gwenllian (died 1136) was the wife of Gruffydd ap Rhys, Prince of Deheubarth, and the sister of Owain Gwynedd. During a revolt which spread through south Wales in 1136, and in the absence of her husband, she led out an army against the Norman English, was defeated and killed. This has led some, rather exaggerating her historical significance, to christen her "the Welsh Boadicea". The field where the battle is believed to have taken place, close to Kidwelly Castle, is known as "Maes Gwenllian". Gwenllian's youngest son went on to become a notable leader, The Lord Rhys.
Gwenllian (June 12, 1282-June 7, 1337) was the only known child of Llywelyn the Last, her mother being Eleanor de Montfort, who died in childbirth. When her father was killed a few months later, Gwenllian came under the guardianship of her uncle, Dafydd ap Gruffydd, until his own capture and execution by King Edward I of England. King Edward, in a display of clemency, allowed the children of Llywelyn and Dafydd to live, the boys in captivity and the girls in convents. Gwenllian was sent to the Gilbertine convent at Sempringham in Lincolnshire, where her death is recorded by the chronicler, Piers Langtoft.
The Princess Gwenllian Society has been formed in honour of the latter princess, and a memorial to her has been erected on the site of the former convent at Sempringham.