The Royal Bank of Scotland (RBS) has confirmed Nathan Bostock will resign from his role as Group Finance Director - less than 10 weeks after joining the board.Bostock, who was appointed on October 1st, has left to join Spanish bank Santander's UK arm as its Chief Risk Officer and Deputy Chief Executive.His departure comes at a critical time as the bank undergoes a comprehensive review and major overhaul in preparation for its return to privatisation. He will remain in his position to oversee an orderly handover of his responsibilities, the state-backed lender said in a statement on Wednesday.Chairman Philip Hampton said: "Nathan did a remarkable job as Chief Risk Officer and was integral to the plan which restored safety and soundness to the bank following the 2008 banking crisis. He leaves with the best wishes of the board."Chief Executive Ross McEwan added: "I had the opportunity to work with Nathan through the autumn as we announced the new capital plan for the bank. He is a talented banker who brought a huge amount to our discussions with our regulators and our majority shareholder. While I'll miss working with Nathan, I look forward to competing with him in the UK market as we strive to better the industry for our customers."McEwan has recently been dealing with a series of issues at the bank, including IT problems which on 'Cyber Monday' caused hundreds of thousands of the bank's customers unable to access their accounts after a computer systems failure.He is also overseeing a pivotal review of the bank's strategy and operations, to be released in February.Bostock was previously head of the company's restructuring and was expected to play a key role alongside McEwan to form a £38bn internal 'bad bank' announced last month.He had also intended to leave RBS to join Lloyds Banking Group in 2011, but decided against the move after Antonio Horta-Osorio, Lloyds' Chief Executive, took a period of sick leave.RD