The two leading runners went the wrong way on the running course, near Green Lake, costing them a chance at the title. A mix-up at a marshal point was said to be the reason behind the costly error.
"I came off the bike in fourth," Bobby said. "During the run I reeled in one guy and I think two other guys went the wrong way.
"I was asking the marshals what position I was in and they said I was third. Then someone said I was first, but I hadn't overtaken anybody."
Bobby, who was a bit surprised after the race, said he was still happy to win the event.
"It is the first time I have gone under 4 hours 30 minutes," he said.
He also competed in the event last year, finishing fifth. He put his improved time and position down to the training and gains he made in the lead-up to Ironman New Zealand, earlier this year.
Jessica was only competing in her second half ironman event on Saturday. After the race, the modest champion said she was never sure of the victory until she crossed the finish line.
"I didn't think I was [going to win], I thought I might get caught the whole way," she said.
Jessica said she was rapt with the victory though and she had a very good bike leg, going into the run in first place.
The Dean parents, Debbie and Bruce, had to do the milking on the morning of the race to free the pair up for the event.
Debbie said her and her husband were rushing through the farm work so they could get down to Rotorua to watch the finish.
She said they arrived just in time to watch Bobby and Jessica win their races, and they were absolutely rapt.
Bruce said they knew the area well and would often stay nearby on Lake Tarawera at a family holiday home.
Bobby and Jessica's next event will be the Tauranga Half Ironman, where they will join number three sibling Gillian at the event.
