Felissi, Filicie, Pelis
In the Prose Tristan, the father of King Mark, whom he preceded as ruler of Cornwall. He also had a son named Pernehan. In Tristano Riccardiano he is the father of Meliodas and Mark. In Tavola Ritonda, Felix was King of Cornwall and Liones. In Malory, Meliodas and Mark were brothers-in-law.
In Tristan, his daughter, Elyabel, becomes Tristan’s mother, while Italian romance says that Felix was the father of Meliadus, Tristan’s father.
Tristan characterizes him as an evil, ruthless ruler who was condemned in the church of Norholt. Italian romance provides an opposite description, calling him a good king. The second son of King Baralis of Cornwall and Lyonesse, Felix became heir to the former when his older brother, Feriando, died as a youth. He was attacked by King Dilianfer of Ireland, who sacked Tintagel, causing Felix to die from heartbreak.
Source
Prose Tristan | 1230-1240
Tristano Riccardiano | Late 13th century
La Tavola Ritonda | 1325–1350
Povest’ o Tryshchane | c. 1580