Zeus and Poseidon had been rivals for Thetis's hand in marriage until Prometheus, the fore-thinker, warned Zeus of a prophecy (originally uttered by Themis, goddess of divine law) that Thetis would bear a son greater than his father.
zˈuːs ænd pəsˈaɪdən hɐdbɪn ɹˈaɪvəlz fɔːɹ θˈɛɾizᵻz hˈænd ɪn mˈæɹɪdʒ ʌntˈɪl pɹoʊmˈiːθɪəs, ðə fˈɔːɹθˈɪŋkɚ, wˈɔːɹnd zˈuːs əvə pɹˈɑːfəsi ɚɹˈɪdʒɪnəli ˈʌɾɚd baɪ θˈiːmiz, ɡˈɑːdəs ʌv dᵻvˈaɪn lˈɔː ðæt θˈɛɾiz wʊd bˈɛɹ ɐ sˈʌn ɡɹˈeɪɾɚ ðɐn hɪz fˈɑːðɚ.