Luke Thompson is to join NRL side Canterbury Bulldogs at the end of the Super League season from reigning champions St Helens.
The 24-year-old is out of contract at the end of the 2020 campaign and has made the decision to continue his career in Australia.
Thompson was man of the match when Saints won the Grand Final against Salford last season, his second title with the team.
If he ever opts to return to the Super League, the England and Great Britain prop would be warmly welcomed back by Saints, who expressed their regret at losing a player who made his debut in 2013 after coming through their academy.
"We accept and totally respect Luke's decision and wish him nothing but success in his career and in his life," Saints chairman Eamonn McManus said on Monday.
"There's no hiding from the fact that this is a bitter disappointment to all of us as Luke has been connected to the club since the age of 11 and has developed into an absolute top player at 24 years old."
Thompson has also won three League Leaders' Shields and made over 150 appearances for Saints, including last week’s emphatic 48-8 win over Salford in a Grand Final rematch that opened the 2020 season.
McManus added: "We are absolutely sure that he will be absolutely committed to the club and to his team-mates for the rest of this season.
"If ever he decides to return to England and to Super League then there would be a red carpet waiting for him at St Helens."
The Bulldogs finished 12th last season and have not made the NRL Finals since 2016.