The forward had a mutual option on his contract to remain at Belmore for 2023, however, the club gave him permission to negotiate.
Hetherington's name has been heavily in the news wire over the past fortnight, with as many as four clubs chasing him. It had been believed that the Knights and Canberra Raiders were the two most keen suitors.
They were joined by the St George Illawarra Dragons and Wests Tigers, although it's relatively unclear how heavily the later duo were being chased.
News Corp are now reporting that Hetherington has decided to join the Knights, with family reasons believed to be the reason behind the injured forward's move north.
It will see the Knights land a second blow on the Canberra Raiders, with the club also reportedly having secured the signature of Adam Elliott, who the green machine were desperate to retain for 2023 and beyond.
The injured forward, who began his career at the Penrith Panthers, has often spent more time off the field than on it with regular suspensions hampering his progress.
A move to the second row from former Bulldogs' boss Trent Barrett was supposed to be part of curbing that problem in 2022, however, a season-ending shoulder injury in Round 3 means the move barely got off the ground.
The powerful forward, who can now play all positions in the forward pack with the exception of hooker, will add more versatility to a Knights' pack still trying to chase Connor Watson, needing to replace Mitch Barnett, and add plenty of depth heading into 2023, with their issues on that front all too clear to see at times in the face of injuries this season.
While the announcement is not yet official from Newcastle, it's understood that it could be so in the coming days.