The pair has maintained a strong relationship, apart of the reason why Titans see potential in him to make a full NRL comeback in 2018.
Rein has been a stand-out in the Intrust Super Cup this year, being named in the team of the year.
Hooker Nathan Peats is all but certain to play in the No.9 jersey next season, after an origin debut this season, however, Rein can be used as a utility on the bench.
The former Dragon played 137 games, across seven years.
He was moved on by St. George to make way for Cameron McIness, and enjoyed a successful season with the Penrith Panthers, despite being restricted to only 5 games.
Rein will add experience and depth to the Gold Coast squad and will work hard towards a starting spot.