Apollo held a grudge against Achilles throughout the war because Achilles had murdered his son Tenes before the war began and brutally assassinated his son Troilus in his own temple.
ɐpˈɑːloʊ hˈɛld ɐ ɡɹˈʌdʒ ɐɡˈɛnst ɐkˈɪliːz θɹuːˈaʊt ðə wˈɔːɹ bɪkˈʌz ɐkˈɪliːz hæd mˈɜːdɚd hɪz sˈʌn tˈiːnz bᵻfˌoːɹ ðə wˈɔːɹ bɪɡˈæn ænd bɹˈuːɾəli ɐsˈæsᵻnˌeɪɾᵻd hɪz sˈʌn tɹˈɔɪləs ɪn hɪz ˈoʊn tˈɛmpəl.