Newcastle have confirmed captain Carl Hayman will join French club Toulon at the end of this season.
The New Zealand Test prop, who moved to Newcastle in November 2007, had been involved in detailed talks about his future at Kingston Park before deciding on a move to Toulon.
"Carl has given outstanding service to Newcastle Falcons during his time here," said club chairman Dave Thompson.
"We held numerous serious discussions about extending his stay with us and made him our best possible offer, but ultimately we respect his decision and wish him every success for the future.
"Carl remains 100% committed to the Falcons for the remainder of the season.
"As club captain, he continues to have a vital role in firstly maintaining our Guinness Premiership status, and secondly helping us to achieve our ambitions of Heineken Cup rugby for next season."
Thompson revealed that moves were already under way to find "an international-quality replacement" for Hayman.
"Clearly, this leaves us with a considerable gap to fill, but Steve Bates and his coaching team have already identified and engaged with a number of potential targets," he added.
"That process remains ongoing, but we are in advanced talks aimed at bringing in an international-quality replacement to continue building on the solid forward foundations at Kingston Park."
Hayman, 30, said: "This has been one of the hardest decisions of my life.
"I would like to thank the club for being so professional in the way they have allowed me the time to make my decision, my team-mates for the manner in which they have welcomed me and the Falcons fans for the affection they have always shown during my time at the club.
"Most importantly, I would like to stress that I remain absolutely committed to the Falcons until the end of the current season, both in terms of securing our Premiership position and then also our dream of achieving a Heineken Cup place for next season.
"My focus will not waiver from those targets at all between now and the summer, and everybody at the club is pulling together enormously to ensure a strong finish to the campaign."