Hull FC have agreed a two-year deal with former Hull KR full-back Shannon McDonnell.
The 25-year-old made 21 appearances for the Robins after joining from the Newcastle Knights in 2012 before his season was cut short by injury.
However, he has now opted to join city rivals to plug the gap created by the departure of another Australian full-back Wade McKinnon.
McDonnell said: "Hull FC is a good place to be, the club are moving forward and they have recruited well for next year so I know I've made the right decision.
"Having Peter Gentle at the club was a big pulling card for me too. He used to coach me when I was younger and I've got a lot of time and respect for him.
"It took me a bit of time to settle in another country this year and the weather makes it a bit of a culture shock when you first come over but I love the city and I just can't wait to get back over there and get things under way."
Gentle said: "To have a player of Shannon's ability come available at this late stage in the year was a real bonus for us.
"He was somebody we had identified earlier in the year when it became clear he would be leaving Hull KR at the end of the season so we moved very quickly once we heard there was an opportunity to bring him to the club."