An overwhelming sense of obligation to return to his family and church in Brisbane is behind Israel Folau's decision to leave premiers Melbourne and join the Broncos.

While the quietly spoken 18-year-old Mormon yesterday insisted money did not determine his decision, it is understood he has rejected a $1 million offer over three years from the Storm to accept a $1.6 million, four-year deal to play with Brisbane from next season.

Another significant move on the player market was being played out last night, with Bulldogs centre Willie Tonga poised to accept a $1.4 million four-year deal with North Queensland so he can play outside former teammate Johnathan Thurston.

But Bulldogs officials have not given up hope, claiming last night they had the right to counter any offer and could make another bid to keep the former Origin and international three-quarter.

Folau's signing - which the Broncos will announce this morning - is sure to add spice to Friday night's match between the two clubs at Olympic Park in Melbourne.

It will also fuel speculation that Storm coach Craig Bellamy is set to follow last year's rookie of the year to the Broncos. Bellamy is widely tipped to replace departing coach Wayne Bennett, even though he has another year on his contract with the Storm.

However, it is understood Bellamy is shattered after advising Folau throughout negotiations to make a decision that was best for him and not necessarily his family.

As reported in the Herald on Saturday, Folau has been torn between being closer to his family in Brisbane, where he shot to prominence with Norths and Queensland, and his desire to stay with his friends in Melbourne.

"It was a very tough decision, the hardest of my life, to leave the Melbourne Storm and sign for the Broncos," Folau said in a Storm club statement. "The club has been like a family to me in Melbourne and without their support I wouldn't have been able to achieve what I did.

"But the opportunity to return home and be closer to my family was too hard to resist. My family is the most important thing in my life and they are the reason I have made this choice."

Last season, Folau repeatedly assured Melbourne he was not leaving the Storm to join Brisbane but he has faced mounting pressure to rejoin his three younger brothers and sister. One of those siblings, David, revealed on the eve of last year's grand final that Folau called him "eight times a day" at the family's Boronia Heights home in Brisbane's southern outskirts.

"Israel's family and church are very important to him and he can be closer to both at home in Brisbane," Storm chief executive Brian Waldron said.

"The impact Israel has made in Melbourne in his short time with the club has been phenomenal and for that he will always be remembered with great affection."

The Storm were surprised at the leaking of the decision yesterday after Folau's manager, Isaac Moses, had put negotiations on hold because of the birth of his daughter.

Folau's decision and Tonga's impending departure mean the cashed-up Bulldogs have missed out on two key signings.

"It was not official yet but moving to the Cowboys was looking that way," Tonga said. "Thurston is the biggest attraction for me, to play outside of him, that is very enticing. He is the best player in the world and it is very exciting to be linking up with him again.

"I played with him in 2004 and to partner with him again is a big plus. But also the Cowboys are a good club, a young club and they are going in the right direction."

Tonga said any suggestions he was homesick and pining for a Queensland lifestyle were wrong: "Townsville is further from Brisbane than Sydney is, I am not homesick or anything."