What is said to be a routinely trite and trashy French novel – The Princess and the President – is due to be published next week with more than the normal fanfare.

This is not because of its storyline: a romance between a fictional French president, Jacques-Henri Lambertye, and a British royal. It is because the author is a real ex-French president, Valéry Giscard d’Estaing, and the royal in question, Patricia, Princess of Cardiff or “Lady Pat”, appears to bear an extraordinary resemblance to the late Diana, Princess of Wales or “Lady Di”.