Kirkwood, who died in 2007 at the age of 86, is the focus of new play Pat Kirkwood is Angry, written by and starring opera singer Jessica Walker, and the show tells her life story, touching on her marriages and divorces and the rumours of an alleged affair with Queen Elizabeth II's husband.
The star was dogged by speculation over her relationship with Prince Philip for many years and even reportedly considered taking legal action to stop the gossip.
Her private correspondence with the royal will be revealed for the first time in the play, after Walker was allowed access to letters written to Kirkwood by the prince.
The notes are now in the possession of royal biographer Michael Thornton, who explains, ""My instructions, in accordance with Pat's will, are that these letters are to be shown to no one except the Duke of Edinburgh's official biographer, after his death.
""Jessica Walker, therefore, has not seen the actual documents, but I have been so impressed by her research into Pat's life that I have drawn her attention to brief significant pages in the letters, and these are what she will be quoting in her play.""
Pat Kirkwood is Angry will premiere at the Royal Exchange Theatre in Manchester, England on Wednesday (03Oct12).