Australia star David Pocock will leave Western Force after the 2012 Super Rugby season, RugbyWA has confirmed.
It is widely expected Pocock will sign for the Brumbies, who finished second in the Australian conference this term.
"While we are disappointed with his decision, we wish David well," the Force said in a statement.
Pocock, 24, joined the Force for their inaugural Super Rugby season in 2006, and has gone on to become a key player for club and country. The openside flanker made his Wallabies debut in 2008, earning 44 caps to date and captaining the team in the absence of regular skipper James Horwill earlier this year.
Force captain Pocock's future at the club had been the subject of speculation following the departure of Richard Graham as coach in April.
Force's hopes of retaining Pocock received a blow when an audacious attempt to lure Will Genia to Western Australia from the Queensland Reds failed later the same month.
Former Leinster and Stade Francais coach Michael Cheika and Waratahs coach Michael Foley have both turned down the chance to succeed Graham, who will take over at the Reds next season.
The Force also said: "For the past six months, RugbyWA has done everything within its power to retain his (Pocock's) services as a leading player within the Emirates Western Force," the Force said in a statement.
"David's concerns were principally around the club's inability to recruit high-profile players with this challenge highlighted by the recent opportunity presented to Will Genia which ultimately was unsuccessful in bringing him to WA.
"This difficulty has since been acknowledged by the Australian Rugby Union in their provision of further concessions for the Emirates Western Force regarding international players for the 2013 season and beyond."