FREMANTLE star Caleb Serong knows that Friday night's preliminary final against Sydney and his younger brother Jai will be a special occasion, but family ties and brotherly bonds will need to be forgotten for 120 minutes.

Caleb and Jai will square off for the third time in their careers, and the second time this season, knowing that one of their teams will be playing in the Grand Final eight days later.

While they have crossed paths sparingly within their previous two AFL games against each other, Friday night's blockbuster preliminary final at the SCG could see the talented brothers spend significant time directly opposed given Jai's accountable midfield role.

Caleb said there was excitement in the build-up, and the pair would come together post-game to support each other whatever way the result went. However, for four quarters, they would simply be opposition players.

"I have thought about it and it's extremely exciting for the family and for both of us to be playing against each other on prelim final weekend. It is pretty special," Fremantle's co-vice-captain said on Monday. 

"It's something that growing up you'd probably think it'd be nice to play with each other and win a Grand Final together, but that's not to be, and we'll be going against each other.

"He's [my] brother and we speak a lot, but at the end of the day he's just another competitor on the other side .

"So for that 120 minutes when you're out there, he's just another jumper, another Swans jumper, another number, and then after the game he's my brother again. But from siren to siren, he's just another opposition player."

Jai Serong was in Fremantle's sights before he was drafted by Hawthorn with pick No.53 in the 2021 national draft, one selection before the Dockers were ready to pounce with their pick No.54.

There was a significant pull to play with his older brother at Fremantle four years later when he made the decision to leave Hawthorn for more opportunities, and he met with coach Justin Longmuir in Perth.

But Sydney won over the 23-year-old, who clashed with Caleb for the second time in his career when the Dockers beat the Swans by 38 points in an extraordinary round 18 game at Optus Stadium earlier this season.

"The first time we weren't crossing paths too much. He was playing key defence (for Hawthorn) and I remember I had to check his run at one point and he raised an elbow at me and gave me a dead arm," Caleb said.

"So that was the first kind of run-in we had. And the second time this year, he dumped me in a good tackle and that was about the only time we kind of crossed paths.

"But I think with him playing a bit more inside mid, there might be a few more opportunities to line up on each other this week, which will be good fun.

"If it happened like that at a few centre bounces and we lined up together, I'd love to get a photo of that. That'd be good fun.

"(But) like I said, he's just another Swans player and I wouldn't be thinking about it too much, except like I would with any other player that I'd be playing on where I'd be looking at how I'd exploit him, how I could beat him."

Serong, who will play his 150th game this week, said Fremantle would embrace a hunter's mentality against Sydney this week, and he would be surprised if Dean Cox's team didn't view themselves as favourites after earning the right to host a preliminary final.

The three-time Doig medallist said the absence of suspended stars Isaac Heeney, Chad Warner and Nick Blakey would not change how the Dockers approach the Swans after their stunning upset win against Brisbane in the qualifying final.

"We're going over there with a really hungry mindset of hunting them and getting after them, and that's the only mindset we really need to take into it," Serong said.

"It's a home prelim final for them. So we're the away team, we've got to travel over there in front of their fans.

"So I'd be surprised if they wouldn't see themselves as favourites, but for us, we don't really read into that. We're just going about playing our footy and going over and hunting them.

"They're a formidable team without those players … and we'll be expecting their absolute best.

"I feel like they're a club and they're a team that thrives at this time of the year, so we're excited for that opportunity and that challenge … and we definitely won't be expecting anything except their best."