LYBEUX. Sir Lybeus is the hero of the romance, Libeaus Desconus, or The Fair Unknown. He is Sir Gawain's son, named Gingelein, and the romance appears in the Gawain cycle, written about 1350.
Sir Thopas, the flower of chivalry, surpasses Sir Lybeux, Thop 900.
Lybeux is one of those names that developed -x in place of -s as a variant pronunciation in Middle English. Others are Amphiorax, Brixseyda, Calyxte. The name appears medially.