Prince Lionel really is a peripheral character. he is mainly notable because he is the tallest recorded member of the english royal family—over seven foot. 

He is important to our story because Phillipa de Roet—Pipa— met Geoffrey Chaucer when they were both in his service. They returned to the Queen’s household after Lionel’s wife died young leaving a baby daughter—yes another Phillipa— to be cared for.