Ulster have signed Australia fly-half Christian Lealiifano on a deal which will run until the end of the Champions Cup pool stages in January.
The 29-year-old will then return to the Brumbies for the start of the Super Rugby season.
Lealiifano has won 19 caps for the Wallabies and recently returned to action after recovering from leukaemia.
He will fill the gap left by Paddy Jackson, who has stepped aside from playing pending legal proceedings.
Lealiifano made Wallabies debut against Lions in 2013
New Zealand-born Lealiifano made his debut for the Canberra-based franchise back in 2008 and earned his first international cap in the 2013 Test series against the British and Irish Lions.
He won his 19th international cap against England in June of last year.
Two months later, Lealiifano was diagnosed with leukaemia but he returned to action for the Brumbies in June.
Lealiifano was born in Auckland before moving to Australia at the age of seven.
The Australian international fly-half expressed thanks to the Brumbies for allowing his short-term move to the Irish province.
"I'm really excited to be joining up with Ulster Rugby and I'm looking forward to getting out there in front of the supporters at Kingspan Stadium," said Lealiifano.
Kiss says Lealiifano arrival 'massive boost
Ulster's director of rugby Les Kiss said Lealiifano's arrival will be a "massive boost" for his side.
"It was paramount that we signed an experienced player to give us another option at fly-half and this is a fantastic solution for us," said Kiss.
"He has overcome significant challenges in his career and that is testament to his bravery and strong character.
"He's a proven leader and we're excited by the influence that he'll have on our young fly-halves Peter Nelson, Brett Herron, Johnny McPhillips and Callum Smith.
"We also have two exciting players in our Academy, Michael Lowry and Angus Curtis, who will also have a fantastic opportunity to learn from Christian."
Ulster start their Pro14 campaign against South African newcomers Cheetahs at Kingspan Stadium on Friday, 1 September.