Kane Cornes is headed into the gruelling fourth and final lap of his second marathon in just five days.

Surrounded by a high-spirited Fat Cat, media crews, and a sea of passionate supporters, the 7NEWS commentator and former Port Adelaide champion is deep into the second and final leg of his punishing double-marathon challenge for Telethon.

Just days after gritting his teeth to complete the massive Perth Running Festival marathon alongside 18,750 participants, Cornes is back on his feet for another brutal 42.2 kilometres.

This time, tackling the picturesque but challenging tracks of Rottnest Island.

As he pounded the pavement along the beach, Cornes maintained a swift 6-minute-per-kilometre pace for a 10km stretch alongside Premier Roger Cook.

The pair paused along the route to grab an ice cream and pose for selfies with eager locals — including a group of fans brandishing a cutout of Fremantle forward Josh Treacy’s head.

The sheer scale of the endurance effort hasn’t been without its humour or hurdles.

At the halfway mark, a winded Cornes turned to the Premier, joking, “I don’t think I’ll make the distance.”

By the third lap, as whales breached in spectacular fashion off Little Armstrong Bay, the physical toll was undeniable.

“A bit banged up, but we’ll get there,” Cornes admitted mid-run.

The course took a joyous turn when Cornes was greeted by a guard of honour formed by local children, with high-fives for every child before the football identity charged straight into a high-stakes goal-kicking challenge.

Joined by four-time Hawthorn premiership hero Luke Hodge, the duo took turns lining up shots at goal to the delight of the roaring crowd.

Hodge slotted his first two kicks smoothly, with Cornes and Hodge trading successful goals.

But it was the kids rallying behind Cornes, chanting his name as he lined up a crucial final kick, that successfully unlocked $100,000 for Telethon.

Not to be outdone, Fat Cat was invited to pull off a goal of his own after receiving a few last-minute tips from Hodge.

Channel 7’s iconic mascot sent the ball right through the middle to raise an additional $100,000, sending the crowd into complete meltdown.

Speaking after completing his run leg, Premier Cook — who admitted to “carb loading” via his favourite Rottnest tradition, a cream donut — praised Cornes’ while joking about his own.

“It was an honour to run with such a superb athlete as Kane, but it was even better to be here for Telethon, raising money for sick kids in Western Australia and doing it in one of our iconic tourism assets. It was a terrific morning,” he said.

When asked if the AFL champion turned broadcaster had slowed his pace to accommodate him, the Premier laughed.

“I reckon, He’s much slower than the time he did on Sunday, but the guy is an incredible athlete,” Mr Cook said.

“We got to run at a decent pace, have a bit of a chat along the way, have a bit of ice cream... I told him a little bit about the island, its incredible history, and the amazing environment that we have here.”

Every step Cornes takes around the island continues to drive massive momentum toward the 59th annual Telethon weekend, which kicks off at RAC Arena this Saturday.

The final fundraising tally from his mammoth double-marathon effort will be revealed live on Channel 7 and 7Plus.