In The Three Caballeros, it is sung when Donald, José, and Panchito are exploring Mexico City at night where they encounter Mexican singer Dora Luz singing in front of them as Donald gets attracted by Dora Luz's singing.
You belong to my heart
Now and forever
And our love had its start
Not long ago
We were gathering the stars while a million guitars played our love song
When I said, "I love you", every beat of my heart said it too
'Twas a moment like this
Do you remember?
And your eyes threw a kiss
When they met mine
Now we own all the stars and a million guitars are still playing
Darling, you are the song and you'll always belong to my heart
(repeat verse and last two lines above)