Harlequins have confirmed that back-row Tom Guest will leave the club at the end of the current season to join London Irish.
Guest will make the short trip from Twickenham to Sunbury to link up with the Exiles on a two-year deal.
Guest came through the Harlequins Academy and made his debut in 2005. He recently played his 200th game for the London side against Cardiff Blues when he also captained the team. He has scored 26 tries over the course of his eight-year career at the club.
The twenty-nine year old has also represented England Saxons in the Churchill Cup games in 2008 and 2009 as well as being named in the squad to face Italy A in February 2008. He also competed in the 2007 Dubai Sevens for England.
"Tom has been one of Harlequins' great servants having recently celebrated his 200th game," said Harlequins Director of Rugby Conor O'Shea.
"I know he is committed to going out on a high this season with the club that will always be his. We would love to have kept Tom for his entire career but the nature of managing a squad within the imposed salary cap regulations involves both accounting for the players you already have and developing personnel within each position."
"I have been at Quins for 12 years and had a great time throughout," said Guest.
"I'd like to thank all the coaches and everybody at the club, with a special mention to Collin Osborne who has been there for me since I was 18 and has done so much for me.
"It was a really hard decision to go, but I am looking forward to the next stage of my career and a new challenge at London Irish.
"Moving to Irish Irish offers a new challenge and I am relishing being part of the new exciting vision that my new club expounds. There is still plenty of rugby to be played this season before moving to Sunbury and that will be my immediate focus."
Irish boss Brian Smith expressed his delight at securing the Premiership-winning forward, who will add huge experience to the Exiles' pack.
"Tom is a title-winning Premiership player with a wealth of experience who has bought into what we want to achieve at this club," said Smith.
"He will be a great addition to our club for two next seasons and yet another key player in London Irish's aspirations to challenge for silverware in the future."