He wrote: “It’s an extraordinary phenomenon to be truly ‘seen’ and ‘known’ by another human, and in Joan, I found someone who innately did both.
“To have loved one another for almost four decades has been the ride of my lifetime.”
The couple married in 1986 and share a daughter, Olivia, and a stepson, Tom, from Washington’s previous relationship.
He also revealed she had been diagnosed with cancer, writing in the newspaper: “Since her stage four lung cancer diagnosis two days before Christmas, she was accepting, clear sighted, sanguine and totally without self pity.
“The oncology team at the Royal Marsden Hospital, NHS nurses, Price’s Mill Surgery and Longfield palliative carers have been beyond exemplary.
“It’s been my privilege to be by your side, sharing our last eight months together, enabling us to say everything we possibly wanted and needed to, so that when you asked Olivia and me two weeks ago ‘to let me go’, we unequivocally said ‘yes’.
“Olivia and I are profoundly grateful for everything that you’ve gifted us with, and we’re relieved that you no longer have to struggle for breath.”
He added: “Our loss is incalculable.
“Your love is immeasurable.
“The depth of our grief is mirrored by the magnitude of our love.
“Do not forget us.”
He also revealed the Prince of Wales came to visit Washington, affectionately referred to as The Colonel, shortly before she died.
He said: “Prince Charles came to see ‘The Colonel’ last month, sat beside her, took her hand and said, ‘It’s been an absolute honour to have known you, Joan’ to which she instantly quipped, ‘I’m still here.’
“Which broke the ice and made all three of us cackle.
“Astonishingly, unlike me, she’s never been star struck and possessed the innate gift of speaking to everyone of any age or status as her equal.”
Washington, from Aberdeen, trained at the Central School of Speech and Drama and had nearly 40 years’ experience in the film industry as a voice and dialect coach, working with stars including Anne Hathaway, Vanessa Redgrave and Emma Stone.
Among her early projects in the mid-80s were Yentl starring Barbra Streisand, Highlander, and The Bounty, featuring Mel Gibson and Sir Anthony Hopkins.
Recent years saw her work on features such as The Witches, where she coached Hathaway for the part of the Grand High Witch, and Yorgos Lanthimos’ black comedy The Favourite, where she worked with Stone.