A version of Mark found in the Icelandic Saga af Tristram ok Ísodd. He was the son of King Philippus and Queen Philippia of England.
When he became king after his parents’ deaths, his sister Blenzibly (Later Tristan’s mother) revolted against him. The short rebellion ended in a truce. Like the early King Mark, he was a noble king, and gave his nephew and wife every benefit of the doubt (and even offered Isolde to Tristan) before he banished them to a cave.
He later gave his kingdom to Kalegras, Tristan’s son, and lived out the rest of his life at a hermitage near Jerusalem. Kalegras and his queen, Lilja, named their second son after him.
Source
Saga af Tristram ok Isodd | 14th century