UFC veteran Georges St-Pierre has vacated the middleweight championship meaning New Zealand-born Robert Whittaker will fight Luke Rockhold in Perth for the undisputed crown.
The 26-year-old has been elevated to UFC undisputed middleweight champion in the wake of St-Pierre's decision to relinquish his belt.
Whittaker won the interim title in July, claiming a unanimous decision victory over Cuban Yoel Romero.
The Australian based Whitaker's clash with former UFC and Strikeforce champion Rockhold, will take place in Perth at UFC 221, on February 11 2018.
Canadian St-Pierre returned from a four-year hiatus last month to stop Michael Bisping in three-rounds to win the title at UFC 217 in New York City.
But the two-time belt holder was never clear about what his future plans were, despite contractually being obligated to unify the belt.
He also confirmed he had been battling with ulcerative colitis, which would keep him on the side-lines indefinitely, which was later echoed by UFC boss Dana White.
The long-time serving president had previously stated he would be "super pissed" if St-Pierre didn't defend the belt against Whittaker.
St-Pierre's decision to relinquish the title means he is the first fighter in UFC history to vacate two championship belts.
Whittaker's new opponent, Rockhold, is coming off a second-round TKO win of David Branch at UFC Fight Night 116 in September.
It was the American's first fight in more than a year after he was stunned by England's Bisping, who registered a first-round knockout win to become the new middleweight champion.
Meanwhile, Whittaker has won his past eight fights, and his last seven since moving up in weight-class from the welterweight division.