South Sydney reluctantly but honourably released Farah on Wednesday, allowing the decorated hooker to sign with his former club for the rest of 2018.

The reunion will allow him to finish his career as a Tiger 18 months after leaving Concord following his ugly fallout with then-coach Jason Taylor.

He was much more warmly welcomed by current coach Ivan Cleary, under whom he will start training this week and be eligible for selection for the next game against Gold Coast on July 1 at Leichhardt Oval.

"Robbie brings a wealth of experience back to the club in a position where we feel we need some additional support at this stage of the season," Cleary said.

"All of my discussions with Robbie have been very positive. He understands the direction that the club is heading in and how he can help contribute to that."

The mid-season switch follows a week of conjecture surrounding Farah's future.

The former NSW State of Origin captain has made only two NRL appearances this season under coach Anthony Seibold after falling behind Origin revelation Damien Cook for the hooker position.

But that was all it took for the 34-year-old to prove he could still cut it in first grade, making 62 tackles three weeks ago against Cronulla and backing it up with a similarly eye-catching display against Gold Coast.

From the Rabbitohs' point of view, it robs the current premiership favourites of a handy back-up.

"He showed his professionalism every single day through some challenging times for him," Seibold said.

"I'm sorry to see him go and, personally, I will miss having him around the team, but our decision to grant him a release is based on what we think is the best thing for him.

"We had a great working relationship and I wish him the best of luck for the future."

Farah himself admitted it was tough to leave Souths after a positive experience but was looking forward to returning to his roots.

"It's not an easy decision for me to leave the club as I've formed many great friendships in my time at the Rabbitohs," Farah said.

"I would like to thank 'Seibs' and 'Richo' (Shane Richardson) for allowing me the opportunity to return to my former club and finish my career there.

"I will forever be grateful for my time at South Sydney and am so proud to be part of the history of such a great club."

Australian Associated Press