Cunobelinus, king of the Britons - Cunobelinus Cynvelin ap Tasciovanus

Mine suddenly says that, too - can’t remember what it was before, but I only follow direct ancestors

Looks like they ran out of verifiable descendants. That tree in its current state is highly suspect for other reasons (too many saints and a Pope who probably doesn't belong).

Cunobelinus, after centuries or oral and written transmission and mythification, eventually sows up in Shakespeare's plays as "Cymbeline", but the name is about the only thing that matches.

+shows up