Los Panchos
Trio Los Panchos is a group from Mexico, not US, They met in NYC In 1944, where they decide to from the group. Two were from Mexico and the other was from Puerto Rico. In 1946, they moved to Mexico City to live and work. They are most famous throughout the world for their bolero/love songs/ballads.
Personally, I can listen and hear whether it is the original group or a later configuration. (just like the Temptations) They are still performing and recording.
Here is their website, though in Spanish. http://www.lospanchos.net/