The Tigers match against Widnes on Sunday will be Dorn’s final game before he hangs up his boots.
The Australian has played 12 season in the UK since his arrival from the Roosters in 2005.
Dorn has scored more tries than any other overseas import in the history of Super League.
The 34-year old has had stints at London, Salford and Castleford.
“It’s really strange,” the Maitland product admitted to Love Rugby League.
“Mixed emotions – very, very sad about leaving but extremely excited about the next step.
“It’s been building up for so long now. I just want to soak it up, enjoy every second and start the next part.”
Dorn will captain Cas and lead the team out at the Jungle against the Vikings this weekend.
Although he has battled with hamstring injuries in 2016, he has still managed 13 tries in 19 appearances along with 21 try assisnts, 18 clean breaks and 58 tackle busts.
Dorn is considering a number of options in retirement but hopes to stay involved in rugby league in some capacity.