Possessing a countertenor vocal register - quite unique in the Portuguese pop panorama at the time of his rise to fame - he distinguished himself in soul and rhythm & blues sounds.
Possessing a voice with a unique register in the Portuguese musical panorama, he joined the formation of Ala dos Namorados as lead vocalist at the invitation of musicians Manuel Paulo and João Gil (formerly a member of Trovante).
In order to cultivate his countertenor voice, Guerreiro attended singing lessons with Maria Cristina Castro, one of the best Portuguese soprano singers.
Carta de Amor also includes an interpretation of "Perdidamente", a poem by Florbela Espanca, put to music by João Gil for a great Trovante hit.
At the Lisbon World Exposition in 1998, he performed in a show in which he recreated Amália Rodrigues, Peter Gabriel, Cole Porter, and Marlene Dietrich.