Michael Grade has resigned his post as Chairman of the BBC, to take up a top post at rival ITV.
His shock departure after just two years in the post took the corporation by surprise, while ITV sources said the company was delighted with the move.
A BBC spokesman said: "Clearly this is a surprise, especially at this moment. For the last two and a half years, Michael Grade has been a great chairman, who along with the director-general Mark Thompson has achieved a successful Charter settlement for the BBC.
"The future system of governance, secured by Michael, will strengthen the BBC's accountability to its audiences. We wish Michael well."