Become of

to come, change, or grow to be (as specified):
he became tired.
to come into being.
to be attractive on; befit in appearance; look well on:
that gown becomes you.
to be suitable or necessary to the dignity, situation, or responsibility of:
conduct that becomes an officer.
become of, to happen to; be the fate of:
what will become of him?
verb (mainly intransitive) -comes, -coming, -came, -come
(copula) to come to be; develop or grow into: he became a monster
(foll by of; usually used in a question) to fall to or be the lot (of); happen (to): what became of him?
(transitive) (of clothes, etc) to enhance the appearance of (someone); suit: that dress becomes you
(transitive) to be appropriate; befit: it ill becomes you to complain
v.

old english bec-man “happen, come about,” also “meet with, arrive,” from proto-germanic -bikweman “become” (cf. dutch bekomen, old high german biqueman “obtain,” german bekommen, gothic biquiman). a compound of be- and come; it drove out old english weorðan. meaning “to look well” is early 14c., from earlier sense of “to agree with, be fitting” (early 13c.).
happen to, befall, be the fate of, as in i haven’t seen joe in a year; what has become of his book? the king james bible has this idiom (genesis 37:20): “we shall see what will become of his dreams.” [ late 1500s ]
in addition to the idiom beginning with become , also see idioms beginning with get