Sylvester Stallone says there is ''no greater pain'' than losing a child.

The 'Rocky' actor has been left devastated after his son Sage Stallone - his 36-year-old son from his first marriage to Sasha Czack - was found unresponsive on Friday (13.07.12) at his Studio City apartment in Los Angeles, and the 66-year-old star has urged people to ''respect'' the later actor's memory.

He said: ''When a parent loses a child there is no greater pain. Therefore I Am imploring people to respect my talented son's memory and feel compassion for his loving mother Sasha.''

Sylvester has ''begged'' for the memory and soul of Sage - who played the actor's onscreen son in 1990 movie 'Rocky V' - to be ''left in peace'' amid speculation of how he died.

He added to TMZ: ''This agonizing loss will be felt for the rest of our lives. Sage was our first child and the center of our universe and I am humbly begging for all to have my son's memory and soul left in peace.''

An initial autopsy on Sage's body, which was completed last night (15.07.12), proved inconclusive and the cause of death is not expected to be known for up to two months until the toxicology tests are completed.

A spokesman for the Los Angeles County Coroner revealed it can take six weeks for toxicology tests to be completed.