Boyzone star Stephen Gately reportedly had an eight-hour-long drinking session and died after choking on his vomit.
The 33-year-old star, who was holidaying with partner Andy Cowles in Majorca, Spain on Saturday, was found dead on Saturday.
Officials investigating the final moments of the gay pop idol are searching for a mystery guest, a 25-year-old Bulgarian named Giorgi Duchev, who the couple are said to have met at a bar and had invited to their home near Port d'Anratx before the singer's sudden death, Sun online reported.
The trio reportedly returned to Gately's flat at about 4.30am on Saturday. An hour later Cowles went to bed but Gately, who had been drinking eight hours, said he would stay up a while longer, the newspaper said quoting sources.
Gately's body was discovered by his partner after midday. Cowles tried to revive the singer for about 30 minutes but sought help from the neighbours after he failed to get any response from the star.
"Andy said he'd screamed, 'Wake up! Wake up!' at him.
He also tried mouth-to-mouth resuscitation. When everything failed he even slapped him across the face.
"But doctors later confirmed Stephen's lungs had filled with fluid. There was nothing Andy could have done. He had drowned and asphyxiated," a close friend of Cowles said.
Police sources say the star's death appears to be natural. "There were no signs of violence or evidence of suicide or any obvious evidence pointing to another probable cause of death, like drugs use. But we're unlikely to be able to shed any further light on what's happened until after a post-mortem."
Boyzone members Ronan Keating, Keith Duffy, Mikey Graham and Shane Lynch said they were "completely devastated by the loss of our friend and brother, Stephen." The members reached Spain.
Gately, born in Ireland, joined the UK based band in 1993 and the band enjoyed great success in 1990s before splitting up in 2000. They reunited again in 2007.
The singer had grabbed headlines in 1999 after he publicly announced that he was gay.
He later married Cowles in a Las Vegas commitment ceremony in 2003.