After a decorated playing career with the Roosters, highlighted by his Clive Churchill-winning display in the Tricolours' 2002 premiership triumph, Fitzgibbon enjoyed a fruitful decade working under Trent Robinson as the club's assistant coach.
But that friendly relationship is on ice this week, with Fitzgibbon, wearing his Cronulla coaching hat, intent on ending the Roosters' season as the Sharks did last year with a 20-10 first-week ambush.
"It was a long time. I've had 10 years working with Trent, so it's definitely a long apprenticeship," Fitzgibbon said ahead of Saturday night's do-or-die battle at Allianz Stadium.
"I had plenty of lessons and am forever grateful for my time there and his mentoring of me to be a coach.
"And he was always supportive and backed me in to take the opportunity when that comes, so I'll be forever grateful for that.
"But this week is about Sharks versus Roosters and, whilst we talk regularly, we're not talking this week."
The latest episode in the pair's coaching rivalry will be the third time in the past four seasons that Cronulla and the Roosters clash in a sudden-death final, with Fitzgibbon and Robinson splitting the first two September showdowns.
The Roosters edged the Sharks 13-12 in 2023 before last year's loss.
Texting is taboo this week, with Fitzgibbon happy to wait until after fulltime to rekindle their great mateship.
"He's fine with that too," Fitzgibbon said.
"He's just as competitive as I am so, no, we'll shut it down this week. We've bumped into each other in plenty of semis now, so it's a contest and it's a game.
"A lot of work goes into a whole season, starting all the way back in the November before, so the ups and downs of the season.
"But you get to this end and it's all on."
Both sides fumbled and bumbled their way into this year's finals, the Sharks losing four of their last five regular-season games with star five-eighth Braydon Trindall sidelined with a dislocated shoulder.
After briefly sharing premiership favouritism after taking down Penrith in round 24, the Roosters also lost playmaker Sam Walker to an ankle injury during a run of four straight defeats.
While below the form that led the Sharks to nine wins from 10 starts before their slump, Fitzgibbon saw enough in last Saturday's 26-16 victory over North Queensland to be heartened.
"We played more like Sharks," he said.
"A bit more cohesion back in. Obviously there were some changes in and out and then we set on the line-up and got back to playing like we know we can.
"It was probably really physical early and we had to stay in the fight there for a bit and then managed to come out the other side and dealt with a couple of disallowed tries and dealt with a little bit of adversity to be able to not get flustered and stick to the plan."
Saturday night's victors will advance to a preliminary final against the Dolphins at Suncorp Stadium next Friday night.
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