The singer was found dead in a hotel room in St Petersburg, Russia, where he had been performing, John Seine said.
Farrell, he continued, had complained of breathing problems before and after the show on Wednesday. The cause of his death has yet to be established.
Farrell, the only male member of the popular four-piece, had been due to perform in Italy on New Year’s Eve.
Born Alfonso Farrell in Aruba, he had been touring with three female backing singers under the name Bobby Farrell of Boney M.
The original Boney M, known for such hits as Daddy Cool and Rivers of Babylon, disbanded in 1986.