Leinster and Ireland back-row Sean O'Brien will join Championship leaders London Irish after the Rugby World Cup.
O'Brien has spent over a decade with the European champions, but the British and Irish Lion will link up with the Premiership hopefuls in December.
The flanker, who turns 32 on Thursday, was selected for the Lions tours of Australia and New Zealand and has won 54 caps for Six Nations champions Ireland.
O'Brien, a European Rugby Champions Cup winner on four occasions and two-time Pro14 title champion, is relishing the prospect of playing for Exiles director of rugby Declan Kidney, who handed him a first Ireland cap in 2009.
"After speaking with Declan it was obvious the ambition London Irish have as a club," he said. "I'm keen to roll up the sleeves and use my experience to help re-establish London Irish as a top club in England.
"It's a club that's been around for a long time and there's an obvious connection to Ireland with some greats of Irish rugby having previously worn the jersey. For now my concentration remains solely with Leinster and Ireland but it's an exciting challenge that awaits."
London Irish can confirm the signing of Sean O'Brien, who will join the club in December 2019. Read more https://t.co/ja7NSoJ4eV— London Irish (@LiRFC) February 11, 2019
St Patrick's Party tickets on sale now from https://t.co/MoQMsaijns pic.twitter.com/l7hr7Hvvsd
London Irish are nine points clear at the top of the second tier after being relegated last year and Kidney says the signing of O'Brien shows they mean business.
He stated: "Recruitment is an ongoing process, and we are always on the lookout for players of Sean's ability.
"Sean has proven himself time and time again to be a quality player who sets very high standards for himself and those around him, he leads by example and has a winning mentality.
"We are delighted that Sean wants to come and be a part of our journey as we move back into West London at the new Brentford Community Stadium in August 2020 after he has finished his commitments to Leinster and Ireland at the end of this year."
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