A Devon visitation makes him a son of Thomas Clifford: http://hdl.handle.net/2027/yale.39002002213917?urlappend=%3Bseq=209 And another work which discusses his genealogy in some detail puts him a further generation back, son of Robert, and brother to the above mentioned Roger: https://archive.org/stream/decontroversiai01scrogoog#page/n451/mode/1up Complete Peerage, (Vol III, page 292) says "Sir Lewis Clifford, K.G., whose curious will (1404) is given by Dugdale, and who is the reputed ancestor of the Barons Clifford of Chudleigh, was probably a br., but certainly not a son, of this Lord". The Lord being referred to is Roger de Clifford b. 10 July 1333, d. 12 July 1389, aged 56. Lewis did have a son Lewis. Nothing is known of what happened to him. Old pedigrees also often suggest he and his wife Eleanor had a son named William. For example see the Devonshire pedigree and Dugdale's Baronage. There are strong doubts about whether William is a son of Sir Lewis. The History of Parliament article for the MP Robert Clifford claims Lewis was even from a Devonshire branch of the Cliffords, and it and many other sources seem to accept it as likely (but not proven) that he was closely related to William Clifford who married Arnold Savage's daughter in Kent. There were similarities in the arms they bore, and also the Kent family used the name Lewis a lot. However, they do not seem to have ever been considered as potential heirs to Lewis's known daughter however.