Insospechable translates to "unsuspected" or "beyond suspicion." It's a less common, more evocative word than a simple "beautiful" or "charming."
In the song, Manuel Medrano sings about a "sonrisa insospechable" (unsuspected smile). This implies a smile that is so pure, genuine, or perhaps unexpectedly captivating that it's beyond any doubt or hidden motive, making it uniquely enchanting to the singer.
Manuel Medrano, a Colombian artist, brings us a song that's all about finding that one person who completely changes your world. He starts by saying he found "Unos ojos tan brillantes como nada que conozcas" [Eyes as bright as nothing you know] when searching the stars, immediately telling us this person is truly special.
This song is a declaration of intense adoration! He's so smitten that she's the "única que me pone a bailar, Que me pone a sudar" [only one who makes me dance, who makes me sweat], and even makes his "corazón a palpitar de una manera agradable" [heart beat in a pleasant way]. He wants to be with her always, promising to be her "almohada y ser tu abrigo" [pillow and your blanket] and to be "Escondidos hasta el fin, ¡Juntos! Donde nadie pueda ir" [Hidden until the end, together! Where no one can go]. It's a sweet, passionate promise to escape the world with the one he loves.