Fanning was reportedly told of his eldest brother Peter's death before entering the water for the third round of the Pipeline Masters at Hawaii this morning.
"It's been a huge day, I've just got some personal stuff going on at home," he said in an emotional interview after his heat.
"It's kind of heavy to talk about right now. I don't know, I'm just cruising, and just trying to live."
Hawaiian surfer Mason Ho also sent his love to the Fanning family, which includes the surfer's sole-surviving brother, Edward.
The death has been confirmed by Fanning's Rip Curl sponsors.
"This is a sad and unfortunate incident and is a private matter for the family to deal with," a Rip Curl spokesperson told the ABC.
"We ask that the media respect their privacy. But we can confirm Mick's older brother Peter has sadly passed away. We will not be commenting further."
Earlier, the Seven Network reported Peter Fanning had been staying at his brother's Queensland home following his recent divorce.
It's believed Peter (43) had three children.
Mick Fanning 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 earlier while competing at the J-Bay Open.
He won his third round heat this morning following the tragic news, and entered the season-ending event at the top of the world rankings.
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.
"And it also makes me think of the years we've had without Sean and how we really stuck together during that time and how beautiful it's been.
"Only the one thing about our family now, especially me, is that I'm much more anxious."
