With the world seemingly in turmoil after COVID-19, she wanted to cheer up her readers by giving them another book centred around her beloved Walsh family characters.
"I had plans to write an entirely different book, but I was finding the world so dreadful and hard post-pandemic. The war in Ukraine and everything else was just too much," she tells HELLO! in our exclusive interview.
"I didn't want to be someone who wrote a book with bad things and bad people, so I wrote something I wanted to read, where any trouble is local and small and can be fixed."
This year is already proving an epic one for the author, who lives outside Dublin with Tony Baines, her husband of almost 29 years. Not only is her 2020 novel Grown Ups being turned into a Netflix series, but - having sold 30 million books worldwide - her portrait is now hanging in the National Gallery of Ireland.
Having turned 60 last September, Marian is finally happy in her own skin after living a life "full of ups and downs" that includes entering rehab for alcohol addiction - she is now 30 years sober and battling depression.
"Turning 60 used to be the age where you were just shuffled off," she says, laughing. "I feel most days that I am a much more confident person than I used to be: I've got so much better at asking for what I want; the fear of people not liking me is dialled down, and I feel kinder to myself in that I don't push myself as hard.
"I used to work all the time, but now there are other things I do. I have hobbies! It was knitting until recently. Before that, I was painting and upcycling furniture. I take care of myself physically and I make time to see my friends and my mother. I prioritise things differently and I like that."
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