The Southampton striker, who has been a revelation during his season's loan stint at Fulham, was expected to tie up a permanent deal with Jean Tigana's Division One champions but the prospect of a return to Portugal has proved too good for him to turn down.
After making his international debut against France recently, the 24-year-old will be hoping for more action at the highest level, and the opportunity to play regularly for Benfica should see him get plenty of opportunities to shine.
Benfica are also signing Internazionale's Pablo Costa and Marco Caneira in the summer, as they look to recover from a disastrous campaign, and mount a serious challenge for the title next season.
Boa Morte has agreed terms on a five-year contract at Estadio da Luz, and the club are also reported to have reached agreement with Southampton over a fee for the pacey forward, rumoured to be in the region of £2.5 million.
Agent Amadeu Paixao insists no deal has been formally signed, stating: "Boa Morte has four great clubs interested in signing him.
"But, for now, we have made no decision."
