Born in Woolwich, she was the only daughter of Major-General Douglas McConnel, an instructor at the Royal Military Academy, and his wife, Ruth Mary (née Garnett-Botfield).

Her work included passing top secret documents, such as plans for a British invasion of Iraq in 1941 to nullify Arab nationalists who believed that the Nazis could help their cause.

[1] The Marquess and Marchioness of Douro would have five children:[citation needed] During the course of her regular work Diana discovered a plot by the Stern Gang to bomb St. George's Cathedral, Jerusalem on her wedding day.

The bomb was retrieved but the couple still received a police escort, which Lord Douro believed to be the standard procedure at the wedding of a general's daughter, his bride not having revealed the plot to him at the time.

[1] The wedding had been precipitated by his posting to Italy and later that year she learnt that he was returning home and arranged to join the same convoy of boats heading to Britain.