London Irish have signed back-row forward Tom Guest from Harlequins in a deal which will see him join the Exiles at the end of the current season.
Guest came through the Harlequins academy and made his debut for the club in 2005.
He recently played his 200th game for the London side against Cardiff Blues - when he also captained the team - and has scored 26 tries for Quins.
Guest said: "I have been at Quins for 12 years and had a great time throughout. 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."
London Irish director of rugby Brian Smith said: "Tom is a title-winning Premiership player with a wealth of experience who has bought into what we want to achieve at this club.
"He will be a great addition to our club for the next two seasons and yet another key player in London Irish's aspirations to challenge for silverware in the future."
Harlequins director of rugby Conor O'Shea said: "Tom has been one of Harlequins' great servants. 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."