“Las Mañanitas” is a traditional Mexican birthday song written by Mexican composer Alfonso Esparza Oteo. It is widely popular in Mexico and other Latin American countries at birthday parties, usually early in the morning to awaken the birthday person.
Since an aubade is “a poem or piece of music appropriate to the dawn or early morning,” Las Mañanitas is an aubade. I learned it in Japan myself. All over the world it is used as a part of the “Cursillo” retreat, when everyone in the neighborhood who has ever “made” a Cursillo gathers on the final morning to awaken those who are just making theirs, with song.
I tried to schedule this so that you, TomCat, would see it soon after awakening, though “the first thing” is probably not possible.