Before her death, Kate, a consultant in medicine for the elderly, hid the card — along with letters and mementos for Chris and other family members — in a box under their bed. In a gesture reminiscent of P.S. I Love You, the 2007 film starring Hilary Swank and Gerard Butler, based on a bestselling novel, Kate had secretly written cards to Chris until the year 2042, the date of his 65th birthday.

Her poignant final act, the story of which has made headlines around the world, was to tell Chris the location of the box, and make him promise to open the envelopes on the dates written on the front.

‘She called it a memory box,’ explains Chris, 41, a supermarket manager from Mirfield, West Yorkshire. ‘She’d never seen the film or read the book — it was just something she wanted to do.