Robbie Henshaw has opted to leave Irish province Connacht for Pro 12 rivals Leinster this summer, on signing his first Irish Rugby Football Union (IRFU) national contract.
Leinster and the IRFU confirmed Henshaw's long-rumoured move to the Dublin province, on a three-year deal which runs beyond the 2019 World Cup in Japan.
Henshaw was given the option of picking any of Ireland's four PRO12 teams having agreed the IRFU deal, and has chosen Leinster, despite Connacht's impressive league form this season.
The IRFU's performance director David Nucifora admitted sympathy for Connacht whilst hailing Henshaw's new deal as another boost for Irish rugby, with the 22-year-old centre remaining on home soil for the entirety of Ireland's 2019 World Cup preparations.
"I am disappointed for Connacht that Robbie has decided to leave but pleased for Irish rugby that he has committed to a further three years," said Nucifora.
"I know that the decision Robbie has taken to move from Connacht is not one he has taken lightly."
Henshaw will offer a significant boost to Leinster's ranks next term, on a day when the club announced 17 contract renewals.
Former Munster lock Ian Nagle will join Leinster from London Irish this summer, while a host of squad mainstays have extended their existing deals.
Ireland internationals Jack McGrath, Mike Ross, Rhys Ruddock, Tadhg Furlong and Dave Kearney are among those extending their contracts with Leinster.
Highly-rated prospects Garry Ringrose and Josh van der Flier have also penned new deals.
Henshaw admitted he had wrestled with the decision to leave Connacht, but ultimately felt choosing Leinster would prove the right option.
"I would like to thank Connacht Rugby, the IRFU and Leinster for allowing me time to consider my future," Henshaw said in a statement on the official Irish Rugby Football Union website.
"This has been a long and difficult process and while I am sorry to be leaving Connacht I look forward to the next chapter of my rugby career at Leinster.
"The support I have enjoyed from the fans in the Sportsground and throughout the province is something that I really value, and I want to thank them for four great years."
Henshaw made his debut for Ireland against the USA Eagles in 2013 and has since won 17 caps, forging a midfield partnership with Ulster's Jared Payne.
Head coach Cullen admitted Henshaw's signature is a tangible boost for next season.
"We are delighted to have secured Robbie's signature for the next three seasons," said Cullen.
"Robbie is a huge talent and we have all seen that over the last few weeks and months with Ireland in the Six Nations and during the World Cup."