Louis Picamoles has sent a farewell message to the Saints supporters, labelling them 'fabulous' and 'incredible'.
The France No.8 is cutting short his stay at Franklin's Gardens as he is joining Montpellier.
Picamoles, who moved to Northampton from Toulouse last summer, still had two years left to run on his three-year deal.
But Montpellier have paid Saints a 'significant transfer fee' and the club have 'reluctantly agreed' to accept.
That means Picamoles, who was crowned Saints' supporters' and players' player of the season after a stellar campaign, will be moving back to his homeland this summer.
But he took time to pay tribute to the backing he received during his time in England.
"I wanted to address this message to the supporters of the Saints," Picamoles wrote on Twitter.
"I discovered a city, a club and fabulous supporters! I spent a very rewarding season as a player and as a man. The reputation of this public is true, you are incredible.
"Thank you for all your unconditional support this season.
"I wish the club and your supporters all the best. You deserve it.