"Sage was a very talented and wonderful young man, his loss will be felt forever," Bega said.
George Braunstein, a lawyer who has represented Sage Stallone for 15 years, said a housekeeper found his body Friday afternoon.
Sage Moonblood Stallone was the oldest of Sylvester Stallone's children and costarred with his father in two films. He was the first of two sons Stallone had with first wife Sasha Czack.
Sage Stallone made his acting debut in 1990's Rocky V and also appeared with his father in 1996's Daylight.
Also in 1996, Sage Stallone and veteran film editor Bob Murawski cofounded Grindhouse Releasing, a company dedicated to preserving and promoting the B-movies and exploitation films of the 1970s and '80s.
"He was very respectful of all the actors in all the movies," Braunstein said. "You couldn't mention a movie that he didn't know everything about."
Mr. Stallone also directed the 2006 short Vic, which screened at the Palm Springs Film Festival.
Braunstein said Mr. Stallone was planning on getting married for the first time, and had frequent requests to work on films.
"He was a full-of-life filmmaker with his whole future ahead of him," Braunstein said. "He was just very up and enthusiastic and positive."