The German has gone back to his native land to sign for Borussia Dortmund.
While the Albion did have the chance to keep Gross for one more season, they listened to his wishes.
In a statement, Albion chairman Bloom said: "In terms of his contribution on the pitch, Pascal goes down as the club's greatest-ever Premier League signing.
"He has been with us since the start of the Premier League era, and has been such a superb player for us.
"He has been a joy to watch and contributed so many important and memorable moments across the last seven seasons.
"I am really sad to see him leave - and I know it has not been an easy decision for him - but I understand his desire to see out his career at the top of the German game with the club he grew up supporting.
"On behalf of all Brighton and Hove Albion fans I would like to wholeheartedly thank Pascal, and I wish him well with Dortmund.
"The term legend is often overused, but in Pascal's case he is a genuine legend of this club and will be welcome back here at any time in the future."
Deputy chairman and chief executive Paul Barber added: “Pascal has been a fabulous professional - on and off the pitch - and has become a friend to many of us at the club. We will miss him greatly.
“However, we also know that the opportunity for Pascal to join his boyhood club was one that was simply too exciting for him to turn down at this stage of his career. We wish him well”.