Stephen Gately's relatives are planning to hire a private investigator to look into the circumstances surrounding the pop star's death five years after he passed away.

The 33-year-old Boyzone singer was found dead in October, 2009 at the home he shared with partner Andrew Cowles in Majorca, Spain.

Officials ruled he was suffering from an undiagnosed heart condition and died from pulmonary oedema - a build-up of fluid on the lungs - which can be caused by congestive heart failure or the early stages of heart disease.

His brother Tony has now suggested the family has unanswered questions about Gately's death and they are planning to hire an investigator once issues with his estate have been resolved.

He tells Britain's The Sun on Sunday newspaper, "We are looking at getting a private investigator once his estate is settled."

Gately's family is embroiled in a dispute with Cowles over the estate, with Tony claiming he is asking relatives to pay for sentimental keepsakes they wanted to hold on to after the star's death.

Tony adds of the dispute with Cowles, "Andy has put a price on every single item that we've asked for. Those things are tarnished now. Some of them were things we had given to Stephen as presents. They were sentimental items... He's had all Stephen's earnings and personal possessions. Our family have had none of that. At the minute it looks like Andy is going to get 60 per cent of Stephen's estate. Our mum and dad will get a fraction, but the estate still hasn't been settled."