The 24-year old, who has represented the Young Socceroos alongside Josh Brillante, completed his signing on Thursday

Versatile, and experienced playing in defence as well the defensive and attacking midfield, Retre says he is excited about the move.

“This is a fantastic opportunity for me to be joining the A-League Champions and double winners,” he said.

“The move has come at an excellent time in my career and to be joining a squad with such quality can only improve my game.

“It’s an honour to be coming to a big club who have had an unbelievable season and I will need to be at my best to break into the side in 2017/18.

“It’s going to be an exciting year, I’m looking forward to playing in the AFC Champions League as well as helping the club win all three domestic trophies.”

Retre was released by Melbourne City after five seasons and Sydney coach Graham Arnold believes the player will boost the Sky Blues' title defences.

“He is an extremely talented young Australian player and will give us even greater competition for places in our squad, especially with an AFC Champions League campaign on the horizon," Arnold said.

“I’m delighted he has agreed to join Sydney FC as I think he will improve us and he has all the qualities to be a top player in this league.

“He is a winner, which is what we like at Sydney FC, and he is hungry for the success which will come his way this season.”

The Sky Blues will return to training in early July, ahead of the club’s huge clash with Arsenal FC on Thursday 13 July.