Amanda MacManus said: "As the person responsible for this unhappy train of events, I cannot with honour remain in this position."

Mrs MacManus's husband James, who is managing director of Times Supplements, added: "I mentioned to a trusted third party, unconnected with journalism or News International, certain information which was then, to my great regret, passed on to the Sun."

In a full statement, Mrs MacManus, 42, said: "It is a matter of great regret to me that chance remarks of mine led to the disclosure in the press of the private meeting between Mrs Parker Bowles and Prince William.

"I am so very sorry for the distress this has caused. Above all, my shame is that I have failed those who demand loyalty and trust, particularly my remarkable employer Mrs Parker Bowles.

"I have been very upset by the rumour and speculation about how the Sun obtained this information and have decided to make this statement to remove the embarrassment and uncertainty that has caused for many people.

"As a result of what has happened, I have today resigned my position with Mrs Parker Bowles.

"I am very sorry to be leaving but as the person responsible for this unhappy train of events, I cannot with honour remain in this position."

Mrs Parker Bowles, who has just celebrated her 51st birthday, said she agreed that Mrs MacManus's position "had become untenable".

A statement on Mrs Parker Bowles's behalf said: "Mrs Parker Bowles deeply regrets that it has been necessary to accept the resignation of Amanda
MacManus.

"Mrs Parker Bowles agrees that her position had become untenable, as Mrs MacManus herself recognised with typical generosity of spirit in insisting that her resignation be accepted.

"Mrs MacManus has given tremendous service and Mrs Parker Bowles will much miss her efficiency, charm and friendship."

A spokeswoman at St James's Palace said: "We are relieved that we can now draw a line under this sad affair."