Ending months of speculation, Brisbane on Wednesday finally confirmed South Sydney mentor Seibold would be their new coach in 2020 and ruled out an early Bennett exit.

In news that incensed some Broncos legends, Seibold will become Brisbane's fourth head coach on a lucrative four-year deal instead of Walters after the club's board unanimously endorsed the 44-year-old at a Tuesday meeting.

And Brisbane said Bennett, 68, would see out his Broncos contract next year before taking up a two-season South Sydney offer in 2020, dismissing talk of a 2019 swap with Seibold.

The likes of Glenn Lazarus and Chris Johns have launched scathing criticism of Brisbane for snubbing former premiership-winning captain Walters.

Lazarus said the Broncos were taking a risk with signing Seibold while Johns described the rookie Rabbitohs mentor as an "unproven coach", accusing South Sydney of choking in 2018.

Carne felt for Walters but wanted Brisbane to get behind Seibold when the club begins life after foundation coach Bennett in 2020.

Next year will be Bennett's 26th and final season with the Broncos reins.

"We all thought Kevvie might get the job but good on Anthony, they are big shoes to fill but he will swallow up that challenge," Carne told AAP.

"Kevvie looked like he would fill the role pretty well but you can't walk away from Anthony now (he is Broncos coach) - you have to support him."

Bennett had not ruled out the Brisbane board asking him to leave 12 months early after falling out with Broncos boss Paul White this year over the club's coaching transition.

But it is believed a 2019 swap stalled, with Brisbane reportedly baulking at paying South Sydney up to $500,000 to allow Seibold to take over the Broncos reins next year.

There were fears Bennett may influence Broncos players such as Tevita Pangai, James Roberts and Matt Lodge to leave for South Sydney with him in 2020 if he stayed on as Brisbane coach next year.

"It's a strange one if they stay at their clubs next year but I don't think it will make a difference," Carne said.

"And I think the Broncos will get behind Anthony when he is here. For Wayne, South Sydney looks like the next challenge he needs."

Ex-Broncos forward Seibold has been linked to the Brisbane job since Melbourne coach Craig Bellamy knocked back a big-money offer to move north in June.

"Seibold will begin a four-year contract in 2020, with current coach Wayne Bennett committed to seeing out his final year as Broncos coach in 2019 - as announced by the club last month," a Broncos statement said.

"The club is looking forward to celebrating Wayne's last season at the Broncos."

Seibold steered the Rabbitohs to the 2018 preliminary final and earned Dally M Coach of the Year honours in his rookie NRL season.

"Anthony was a stand-out. His football knowledge is exceptional, as is his thinking and process around people management," Broncos chairman Karl Morris said.

Australian Associated Press