Sharecast - The insurer said Turner had fallen short of the "high standards" the group sets itself "on this occasion".
Prudential (LON:PRU) gave no details of the incident but said it has no implications on the group’s financial performance, reporting or operations.
The company, which has appointed Ben Bulmer to replace Turner, said the latter will remain available to it for four months to support a smooth transition.
Prudential said that Bulmer, who is currently the CFO of insurance and asset management, would bring much experience to his new role. He has extensive experience of the group, having served in a variety of leadership positions across the finance function in Asia and London since joining in 1997.
Bulmer will become a member of the Group Executive Committee, reporting to chief executive Anil Wadhwani, and will continue to be based in Hong Kong.
Wadhwani said: "Ben is a highly experienced finance leader who has developed a deep understanding of our business and markets during his 26 years at Prudential, including in his role as chief financial officer at Prudential Hong Kong's Life Insurance businesses and in central finance roles in the group.
"Our Code of Conduct sets out that we expect all our colleagues to adhere to the highest professional standards and behaviours. On behalf of the board, I would like to extend our gratitude to James for his twelve years of contribution to the business and wish him well for the future."
At 0920 BST, the shares were down 2% at 1,102.50p.