"Isn't She Lovely?", the song he wrote after the birth of daughter Aisha. The song even contains sounds from Aisha's childhood. It's so heartmeltingly sweet that it's legendary.
In James Corden's 'Carpool Karaoke', James makes a request of Stevie that he admits is unusually indulgent: he asks Stevie to call his wife and sing "I Just Called To Say I Love You". Stevie happily does so, changing the lyrics to "say James loves you", leaving James clearly quite close to tears.