The 24-year-old, an outspoken advocate for the LBGT+ community, was gunned down on Thursday as he rode a motorbike in the capital San Juan.
Police said he was shot eight times and was taken to Rio Piedras Medical Centre, where he was pronounced dead.
His murder is the 24th in Puerto Rico in the first 10 days of the year, according to El Vocero, one of the largest newspapers in the US Caribbean territory.
In a statement, Fret’s manager said: “Kevin was an artistic soul, a big-hearted dreamer. His passion was music, and still had a lot to do.
“This violence must stop. There are no words that describe the feeling we have and the pain that causes us to know that a person with so many dreams has to go.
“We must all unite in these difficult times, and ask for much peace for our beloved Puerto Rico.”