The adjectives "beau", "nouveau" and "vieux" has in Masculine Singular form, peculiar forms when written before a noun that starts with a vowel (or vowel sound, like homme). I'll compare it to "livre":
Un vieux livre ("standard" adjective) des vieux livres (plural)
Un vieil homme ("Special form") des vieux hommes (plural - again)
Only the singular form is affected and the same counts, as I mentioned, for "beau" and "nouveau". Their forms are "bel" and "nouvel" :)