When Richard E. Grant was 10 years old, he fell asleep in the backseat of the car. Upon awakening, he saw his mother and a friend of his father’s having sex in the front seat.

This was obviously traumatic, so Grant, having no one he could talk to about it, started keeping a diary. It is a habit that Grant, 66, has maintained ever since. His past diaries produced two fun books about his day job: “With Nails: The Film Diaries of Richard E. Grant,” which takes its name from his breakout role in “Withnail and I”; and “The Wah Wah Diaries,” about directing an autobiographical movie, “Wah-Wah.”

But his writing never meant more to him than it did between December 2020, when his beloved wife, Joan Washington, a highly acclaimed dialect coach, was diagnosed with cancer, and the following September, when she died.

Richard E. Grant and Joan Washington on their wedding day in 1986. Before she died, Washington told the actor to find “a pocketful of happiness” each day.

(Photo from Richard E. Grant)

“Your memory forgets stuff and tricks you, and I wanted to have a record of every day and every stage we went through together,” says Grant, whose new book, “A Pocketful of Happiness,” charts those terrible times but also explores their 38 years together. “My diary was a way of trying to hold on to and capture all that.”

It was also important for Grant to capture the generosity of the 99% of his friends who “stepped up and were beyond extraordinary” throughout the crisis, including famous ones like Gabriel Byrne. (“The one percent who didn’t are the ones I’ll never speak to again,” he says vehemently. “I will cross the road and I will blank them.”)

Grant initially refused approaches from publishers this time, but his daughter thought it would be good for him. He agreed to do it only if he could avoid it being “all doom and gloom.” So the book encompasses their full relationship, alongside stories from his career, weaving in his experience making “Can You Ever Forgive Me” with Melissa McCarthy and the Oscar nomination that followed — as well as encounters with Barbra Streisand, whom Grant has been obsessed with nearly his entire life.

Speaking recently by video from his home in England (with the background blurred because “I’m a lifelong hoarder and everything is floor to ceiling stuff”), Grant is alternatively pensive about his wife and charmingly chatty as we discuss celebrities we admire. In other words, the book is an accurate reflection of Grant in real life.

This interview has been edited for length and clarity.

Is it difficult talking about her illness and death all over again now, doing press for the book?

I’m grateful to be talking to you about our life together while sitting in the room where she taught actors. People who are grieved want to talk about the person who is gone. But I don’t want to talk about the suffering part without the other 38 years.

You write that you “travel in hope.” Did that help with this ordeal or did all this change you?

It profoundly changes you, obviously, but your essential nature is unchanged. My DNA glass is three-quarters full now.

You become very conscious of living in the day, for the moment, knowing that time is running out. But there’s a parallel track where the level of exhaustion that the person who’s dying has is so overwhelming.You want them to be relieved of it but you want to hold on to every minute you still have. It’s a fierce mental and emotional battle. But still, I traveled in hope.

Joan’s parting charge for you was to find a “pocketful of happiness” each day. Was that doable in the early days of grieving? What about now?

I’m conscious of trying to follow her mantra and it has been incredibly helpful even though there are days you are tsunamied by grief. I just sold our summer home in France that we had for 35 years and it feels like a second bereavement.

Somebody who read the book carved the title in wood for me so I have three of those around the house as reminders. And I have it on my laptop and my phone.

You write about “memory-charged” objects that you bought together. Do they lose their power without her there with you?

I feel like it’s an ongoing conversation, and I feel reassured by having all of the stuff and all the stories around them.

It’s like how I was so grieved by that idea of not being able to share my day with her in all the detail, [telling her about details like]: Is that an Edward Hopper behind you and a baseball bat on the wall? But then I thought that after 38 years I know what her response would be, how she’d be analyzing your accent in Brooklyn. So it’s still an ongoing conversation. Please know that I’m not saying out loud, “Oh, I said to Stuart…” but in my head it’s still there and I find that a very reassuring way of dealing with this loss.

Grant, third from left, on the set of “Spice World” with the Spice Girls. The actor confesses to being “an inveterate name-dropper.”

(Photo from Richard E. Grant)

In “The Lesson,” your latest film, you play a father and husband who is a horrific bully, yet he’s also dealing with a deep personal loss. Was that a challenge or was it cathartic?

It was my first job with real substance after Joan died and playing the loss was a good way of channeling and dealing with grief.

Was it tricky to shift from writing about Joan’s radiation to, say, an encounter with Jennifer Aniston or Sting?

I am an inveterate name dropper as you have just very politely pointed out. I left it to the editor to decide whether something was too much of a weird gear shift and she just said, “That is a reflection of how your brain works.”

How much did you edit or rewrite the diary entries for publication?

A diary is not written in the twilight of your life looking back where you can “rosy-glowsy” something and re-edit and re-imagine what happened. In a diary you don’t know what’s coming tomorrow, and that’s what gives it the immediacy and authenticity and value. Nothing was revisited afterwards in the diary entries.

And when I was seesawing backward in time I also relied on diaries and our letters rather than trying to fashion something fancier out of it. I think you would sniff that out very fast.

I found an old biscuit tin that I thought had a piece of Christmas cake left in it, but I found a stash of letters that Joan and I had written to each other. Finding that cake tin stuffed with letters, I could hear her voice was so powerful. It was absolutely golden. I was so thrilled, and, of course, heartsore, but joy overwhelmed the sadness.