Mick Fanning's mother says Peter died from an enlarged heart

Mick Fanning’s mother, Elizabeth Osborne, has spoken out about her son Peter ending speculation that drugs were the cause of his sudden death.

Peter Fanning died in his sleep after suffering from a "serious hyperthyroid disease" that had almost killed his father three years earlier, according to reports.

The 43-year-old was found dead inside a Tweed Heads home early morning December 16, just hours before his world famous younger brother paddled out to surf for a fourth world title.

On the day of his funeral Ms Osborne silenced suggestions that her son's death involved drugs, revealing that Peter's autopsy states that he died from an "enlarged heart," The Gold Coast Bulletin reported.

Ms Osborne said her son had been on heart medication and eating a healthy diet since the scare, up until he was found dead in his apartment saying it was too difficult to talk about the incident in detail.

“I can’t do it — I am too devastated,” she said in a text message.

Family and friends will say their final goodbyes to the father-of-three at a funeral service at the Tweed Heads Crematorium at 11.40am on Tuesday.

The Australian surfing champion has endured a number of personal hardships throughout his career.

In 1998, he delivered the news to his mother that another brother, Sean, had been killed in a car accident.

He also narrowly survived a near-death experience himself this year, fighting off a shark attack in South Africa while competing at the J-Bay Open.

In August, Fanning's mother Elizabeth Osbourne told 60 Minutes of the pain of losing a child and how she feared it would happen again when Mick fought off the shark.

"I thought, the universe can't be this cruel," she said.