Harlequins have confirmed that Tom Guest will leave the club at the end of the season to join London Irish.
The back row, 29, has been with Quins for 12 years, having come through their academy and made his debut in 2005.
“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.”