The Knights announced two weeks ago that they had signed Boyle, a two-time NRLW premiership winner and the incumbent joint Dally M medallist, along with another former Brisbane Broncos teammate, Tamika Upton.

It's believed Elliott told his Raiders teammates on Sunday of his departure, before Newcastle confirmed on Monday that Boyle's boyfriend had accepted a three-year contract, starting next season.

"We're very pleased to have signed Adam for 2023, '24 and '25," Knights chief executive Phil Gardner told ACM.

"He's a tough, very competitive and experienced forward, and we're delighted he'll be joining us.

"And obviously it's a nice story that he and his partner Millie Boyle are going to be playing for the same club."

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Gardner was confident Elliott would prove an "ideal replacement" for rugged Mitch Barnett, who has signed a three-year deal to join the New Zealand Warriors.

Elliott has played in 112 NRL games for Canterbury and Canberra, and represented both NSW Country and the Indigenous All Stars.

The 27-year-old started his top-grade career with the Canterbury Bulldogs in 2016, and played three seasons at Belmore Sports Ground alongside Knights enforcer David Klemmer.

"Obviously with Barney leaving, that's going to leave a pretty big hole but with Adam coming, that hole is not quite as big any more," Klemmer said.

"He'll be a good, handy pick-up for us."

Gardner was confident Elliott's reputation for dubious off-field incidents would not be an issue at the Knights.

Less than 12 months ago, he was sacked by the Bulldogs after a much-publicised tryst with Boyle in the toilets of a Gold Coast restaurant.

The NRL fined Elliott $10,000 for bringing the game into disrepute and failing to comply with biosecurity protocols, and issued Boyle with a warning - although she insisted all they did was exchange kisses.

The Raiders took a chance on him for the 2022 NRL season, signing him for a "fresh start" in the capital on a one-year deal.

Elliott had previously been involved in a scandal at the Bulldogs when he was photographed dancing naked at Sydney's Harbour View Hotel during the club's 2018 Mad Monday celebrations.

On that occasion, he was fined $25,000 and subsequently pleaded guilty to wilful and obscene exposure in Downing Centre Local Court.

Elliott escaped a criminal conviction but Deputy Chief Magistrate Jane Mottley described his behaviour as "disgraceful to yourself and any standards of decency".

Gardner was confident Elliott, who by all accounts has not put a foot wrong since joining Canberra at the start of this season, had learned from his mistakes.

"All his references have been strong," Gardner said.

"We know that he's in a long-term relationship and we're confident he'll be a good representative for the Knights."

Meanwhile, the Knights are still waiting to learn if five-eighth Anthony Milford will extend his stay beyond the end of this season.