The 25-year-old Parramatta full-back played for the Fijians at the last World Cup in 2008 when they reached the semi-finals, an experience that changed his life for forever, and was looking forward to teaming up with them again five years on.
But the call of the Kangaroos was too difficult to resist and Hayne will win his seventh cap against Fiji at Langtree Park.
"It's obviously going to be an emotional game but I'm excited and looking forward to it," Hayne told Press Association Sport.
"Everyone pretty much knows what it did to my life in 2008 and how it changed it.
"I will always honour it because it was a great experience.
"My heart will always be with Australia but my soul will always be with Fiji.
"It was a bit of a shock making the Australian team. I thought I would be playing for Fiji. I always knew I was coming to the World Cup, I just didn't know which team I was playing for."
Hayne, whose Fijian father Manoa Thompson had a season with Warrington in 1995-96, caught up with the Pacific Islanders after their opening match against Ireland in Rochdale on Monday and admits he will be sorely tempted to join in their traditional hymn singing before kick-off on Saturday.
"I spent a bit of time with them and caught up," he said. "We had a laugh."
Leading Fiji is former Australia Test forward Petero Civoniceva, who was on the winning side against Hayne in that semi-final of 2008.
Civoniceva, who won 45 caps for the Kangaroos, retired from the NRL at the end of the 2012 season but played on this year with his old club Redcliffe Dolphins to keep himself fit for the World Cup.
"He's on the other side now," Hayne said. "He's enjoying doing what I did.
"He's a legend in Australia and he's a legend in Fiji as well. To see him playing at the weekend was tough. I would have loved to have been out there with the boys."
Hayne will be on the wing on Saturday, with Greg Inglis getting the full-back spot in the absence of Billy Slater, who is one of seven players rested from the team that began the campaign with a 28-20 win over England at the Millennium Stadium.
Forwards Boyd Cordner and Josh Papalii will make their Australian debuts.
Fiji coach Rick Stone is set to stick with the team that won 32-14 against the Irish, although Catalan Dragons centre Daryl Millward is hoping to force his way into the side after being omitted from the 19 on Monday.
The Fijians lost 52-0 to the Kangaroos in that semi-final in Sydney five years ago and threequarter Sisa Waqa, who will be up against his Melbourne captain Cameron Smith, admits they face a difficult task on Saturday.
"You have to give yourself a chance in matches against Australia and you have to be able to go at them for the full 80 minutes," Waqa said.
"The main thing for us is to make sure we play our game right. It is important to cut out our errors."
Ireland were shocked by the initial ferocity of the Fijians' defence and Hayne says the Australians will be bracing themselves for a bruising opening quarter.
"It's going to be physical," he said. "The first 20 is going to be tough."
Australia: G Inglis; J Hayne, J Morris, M Jennings, D Boyd; J Thurston, D Cherry-Evans; M Scott, C Smith (capt), J Tamou, L Lewis, J Papalii, N Myles. Subs: B Cordner, R Farah, A Fifita, P Gallen.
Fiji: K Naiqama; M Koroibete, S Waqa, W Naiqama, A Uate; A Noilea, A Groom; A Sims, J Storer, P Civoniceva (capt), T Sims, J Bukuya, K Sims. Subs (from): A Koroisau, E Vunakece, K Evans, V Junior Roqica, D Millard.
Referee: R Silverwood (England).
- Sports & Recreation