Brad Thorn is a big man with even bigger dreams but even he admits his All Black renaissance defies belief.

The former NRL star is shaking his head and pinching himself at the same time as he prepares for Saturday night's Tri-Nations decider at his old, much-loved home ground.

The ex-Bronco and Kangaroo thought his representative career was over when he crossed codes and countries for the second time 12 months ago but not only will he play at Suncorp Stadium, he's also expected to be a key figure.

"This is crazy," Thorn said. "I had a dad that inspired me to have big dreams and stuff but this is just ridiculous.

"Now at 33 years of age, even I couldn't dream of this and, as I say, I have big dreams otherwise I would never have come across earlier on.

"I've been excited about this for a while back and there's a lot riding on this game so it makes it even better."

Thorn's story is unique to rugby history: Born in NZ and raised in Brisbane, he grew up cheering for the All Blacks but aspiring to play for the Broncos and Queensland in league.

"I used to go to Ballymore (to watch Bledisloe Cup Tests) and had many fond memories," he said. "The All Blacks usually won and it was pretty good fun."

An Australian league international and three-time premiership player, he switched to union for the first time in 2001 but passed up the chance to play for New Zealand when selected later that year.

After 12 months off, the converted lock returned in 2003 and helped the Crusaders to the Super 12 final and rode the wave through to All Blacks selection, playing in all 12 Tests.

Three more seasons at the Broncos from 2005 was topped by the 2006 premiership, and when he returned to rugby this year and played in the Crusaders' Super 14 final win over NSW, he became the first man to win both the NRL and Super rugby titles.

Thorn has no doubts the Wallabies will be smarting from their last-start 53-8 thumping by South Africa and expects his Crusaders coach, Robbie Deans, will have them ready to fire.

"The thing that I loved about Robbie, and the thing I loved about Wayne Bennett was they both hated losing and both loved winning, which is probably similar to me," he said.

"He wouldn't have enjoyed that. I've heard people say they weren't committed but the one thing I know about Robbie is he wants to win every game. Squash, tennis, whatever.

"It would have been a huge, big wake-up call for them and they would have copped a lot of grief so that makes them really, really dangerous so we have to make sure that we're hungry."

As with most former Broncos, Thorn credits Bennett as a major influence on his career but another conversion hasn't stopped the veteran league coach assisting him.

He has no doubt a character reference from Bennett helped minimise his suspension to one week from a dangerous tackle which ruled out Springboks skipper John Smit in July.

"He wrote a nice little letter for me, so that was good. It was nice to have an old mate that I could call up," said Thorn, who will play on next year at least.

If Thorn copped the suspension South Africans were crying out for he probably would have missed Saturday night's high-stakes Test, robbing him of his first chance to play Australia in the town he calls home.

The damaging 113kg, 195cm forward has one rugby Test on the ground, in the 2003 World Cup when Tonga interrupted the All Blacks haka with their own war dance.

"It's one of my favourite haka experiences. Tonga and us had a haka-off and basically finished touching noses by the end of it. It was a lot of fun and the crowd enjoyed it."

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