Eggs are a method of reproduction in certain species whereby the offspring develops outside the body.The sorceress Nimueh created an Afanc, magically transporting it inside an egg to the water supply of Camelot, where it hatched and caused a plague. Eventually, Arthur's manservant, Merlin, and the court-physician Gaius discovered the Afanc. With the help of Arthur Pendragon and Morgana, Merlin was able to destroy the creature using his own elemental magic (The Mark of Nimueh).
Dragons hatch from dragon eggs, having been called into the world by a Dragonlord. Following the Great Purge, all but one was destroyed. Merlin and King Arthur Pendragon set out with the Knights of Camelot; with the latter two wishing to destroy it and Merlin (a Dragonlord) wishing to rescue it and return it to Kilgharrah - the last surviving Dragon. Merlin was successful in his goal and the Dragon was born. Merlin named it Aithusa (which means 'light of the sun") and Kilgharrah noted that, as a white Dragon, it was indicative of good times to come for Camelot (Aithusa).