Washington had worked with some huge stars in her long career, from Cate Blanchett to Ewan McGregor.
However, before her death on September 2, Grant spoke of the joy of working with her on the adaptation of the hit stage musical.
In an interview with Newsweek, Grant explained how he had a great deal of new skills to learn on the set, including playing an all-singing, all-dancing drag queen.
But part of the movie also meant he had to nail a very specific British accent.
He told Newsweek: “He [Jonathan Butterell] was very persuasive and he said, ‘We’ll get a great team of people around you,’ which he did. I said, ‘What about the Sheffield accent?’
“He said, ‘Well, I’m from Sheffield. They said your wife, Joan Washington is a celebrated dialogue coach in England. Learn the Sheffield accent from her.’ So, that’s what I did, and then he assembled a team around me.”
The team included choreographer Shaun Niles and costume designer Guy Speranza, but Washington was at the heart of his performance, helping him nail the voice of his character Loco Chanelle.
Speaking more of what Washington helped him achieve, he said of the Sheffield accent: “I tried to stay in it as much as possible when I was in Sheffield. I think, inevitably, you’ll fall into the vernacular and the rhythm of how people speaking there, so, I loved it. And people were very accommodating and hospitable towards me.”
On September 3, Grant shared a video of him singing and dancing with Washington, with a caption which shared the sad news about her death.
He wrote: “ONLY YOU! Joan - Love of my Life, giver of Life to our daughter Olivia. Our hearts are broken with the loss of your Life last night. 35 years married and 38 together. To be truly known and seen by you, is your immeasurable gift. Do not forget us, sweet Monkee-mine”
Many stars posted to his Instagram to share their condolences, such as actor Emily Mortimer commented on his post: “I can’t believe this sad news. Sending so much love to you both. And thinking of you so much. Joan was incredible. One of the world’s great teachers. It was a privilege to know her and have been in her orbit. And your guys’ love story is just an inspiration”
Nicholas Hoult added: “What an amazing couple. Love you and Joan, the time spent with you both was truly magical. I can never thank her enough for all her kindness, the lessons she taught me and the memories I’ll cherish. Sending you so much love”
Lena Dunham said: “To know you and Joan together has been a gift to all who have encountered you. Thank you for your gorgeous example of connection and team work, an inspiration to us all. The fiery and dynamic Joan will be in my heart as I hold you and Olivia there too. Love you so, REG”
Many others who have worked with Washington shared their tributes to her on their own social media accounts.
Jessica Chastain wrote: “My heart is broken. Joan Washington had such a profound impact on me, yes as an artist, but mostly as a woman. I’ve looked toward her. Her strive towards excellence made her the celebrated dialect coach she was.
“We worked together on The Debt, Poirot, Coriolanus, Miss Julie, Crimson Peak, The Zookeeper’s Wife, & The 355. Every day I was excited to go to work and giggle with Joan. She was a barometer of truth with a wicked sense of humor. I loved her very much.
“The way she celebrated her family has been very meaningful to see over the years. My heart goes to her beloved Richard and Oilly. You were always her North Star.”
The British National Theatre also paid tribute to her, saying she had contributed to more than 80 productions.
