Patroclus never saw him coming,
moving across the deadly rout, shrouded in thick mist
and on he came against him and looming up behind him now –
slammed his broad shoulders and back with the god’s flat hand
and his eyes spun as Apollo knocked the helmet off his head
and under his horses’ hoofs it tumbled, clattering on
with its four forged horns and its hollow blank eyes
and its plumes were all smeared in the bloody dust.
Forbidden before this to defile its crest in dust,
it guarded the head and handsome brow of a god,
a man like a god, Achilles. But now the Father
gave it over to Hector to guard his head in war
since Hector’s death was closing on him quickly.

– Homer

The Iliad, Book 16, lines 917-929. Apollo knocks Achilles’s helmet off Patroclus and Zeus gives it to Hector to protect his head, as Hector’s death is said to be closing on him quickly. This foreshadows that Hector has not long to live, for while he escapes immediate death at the hands of Patroclus, he will soon be killed by Achilles in revenge for his friend’s slaying.