It’s impossible to predict exactly what will emerge on publication of a biography but, rest assured, someone will tell you something you wish you had known before.

So, the letter that arrived telling me of the existence of a beautiful portrait of one of the key characters in my biography of Wallis Simpson, Mary Kirk, was both a thrill and not exactly a surprise. This week I travelled up to Edinburgh to see it.  It is a large (3.5 X 4 ft) pastel,  apparently commissioned by her soon-to-be husband,  the dashing Frenchman Jacques Raffray and, according to family lore, painted from photographs. It was intended as an engagement present for Mary and Jacques but never sent to America. The artist was Raffray’s aunt  ‘Minnie’ Rutherfoord – (Minnie’s sister had married Jacques father)-  a professional with a number of works accepted for the Royal Scottish academy exhibitions between 1895-1920. This was to be the last one she showed there in 1920 and bore the rather curious title ‘Down in the Forest’ curious because the background is more of a lake than a forest.

I had always known Mary Kirk was beautiful but the only pictures I  could find for my book showed her in her middle years.  Still attractive but rather matronly, the inevitable (and fashionable)  cigarette dangling from her fingers. This portrait would have been much more striking and perhaps better explained her story. She was a childhood friend of Wallis but travelled in Wallis’s slipstream and manipulated by her. Eventually, when Wallis was looking for someone to occupy husband Ernest while she was off on holiday with the King,  Mary and Ernest fell in love. It’s not hard to see why.

The picture, approaching its own centenary, is in good condition although a little faded. Moving or cleaning it might destroy it. The present owners , relatives of the artist, have always known something of the sitter’s history but  it was seeing Mary Kirk in C4’s The Secret Letters, the recent documentary based on my book,  that stirred them to contact me in the hope of discovering other Kirk relatives .

I have puzzled over why this beautiful portrait  was never sent to Baltimore. Perhaps its size or delicacy made that difficult but surely not impossible. Or was it because the marriage between Mary and Jacques soured more quickly than I realised?  I doubt this because Mary always wrote in affectionate terms of Jacques, even as she contemplated divorcing him. But who knows? I am certain that,  had Mary known of the portrait’s existence once she married  Ernest in 1937 and was living in London and especially after a warehouse fire destroyed many of their most precious possessions,  she would have wanted it in their house in Upper Phillimore Gardens. Mary  died of cancer in 1941 leaving a two year old son who later changed his name and moved abroad.  He too never knew anything about the portrait,  which has now acquired a life and a story of its own.