Ajena translates to "belonging to another" or "someone else's." It's a key word in this song, capturing the central conflict of unrequited love and forbidden desire.
The singer is deeply attracted to someone who is already in a relationship, making her "ajena" to him. This word perfectly encapsulates the bittersweet longing and the impossibility of their connection, as he laments, "Lástima que seas ajena" (It's a shame that you belong to someone else).
Have you ever been completely smitten with someone, but they're already taken? That's the bittersweet ache Los Tigres Del Norte sing about in "Lástima Que Seas Ajena" [It's a Shame You're Taken]. The singer is totally captivated, confessing, "Me gustas completita tengo que confesarlo" [I like all of you, I have to confess it]. Just saying hello gives him "el mal del amor" [the sickness of love], and his mind races with beautiful, vivid images of what could be, even though he knows it's impossible.
He's so taken that he declares, "Por alguien como tú por Dios que dejo todo" [For someone like you, by God, I'd leave everything]. But the harsh reality keeps hitting him: "Lastima que seas ajena y no pueda darte lo mejor que tengo" [It's a shame you're taken and I can't give you the best of what I have]. He feels like he arrived too late, wishing he had the "llave para abrir tu cuerpo" [key to open your body]. It's a passionate, almost desperate longing for a forbidden fruit he can't taste, dreaming of taking her "al mismo cielo" [to heaven itself].