Picamoles returns to Montpellier
Northampton said the 31-year-old Picamoles had "received a proposal from Montpellier which will underpin the future financial stability of his family."
"The club has therefore reluctantly agreed to the transfer and accepted a significant transfer fee for his services. This fee will be reinvested into the playing squad to ensure Northampton Saints continues to strive for success on the pitch," Saints said in a statement.
Picamoles, who had signed a three-year deal with Northampton last summer, added: "I am proud to have played for Northampton Saints and I have enjoyed my time with the club. I am grateful for all the support and friendship I have received from the club, the coaches, my teammates and supporters."
Capped 61 times by France, the abrasive forward came through the Montpellier youth section and quickly made his name at the southern club before leaving for Toulouse in 2009.
"Montpellier approached me to know if I had the desire to return to France. It coincided with the French rugby federation's desire that French internationals play in the Top 14. I left for three years in England, but I jumped at this chance, which was tough to refuse at the age of 31," he added.
Montpellier captain Fulgence Ouedraogo came through the club's youth ranks alongside Picamoles.
"He is my childhood friend and I'm very happy to be able to play once more with him next season. It's also a standout recruit for Montpellier because for me, he's one of the four best No.8s in the world," Ouedraogo said.
Montpellier, knocked out of the Top 14 semi-finals last week, will be coached next season by former Clermont and Scotland manager Vern Cotter – the Kiwi taking over from South African Jake White.
Agence France-Presse
