The Withnail and I actor's beloved spouse Joan Washington died in September 2021 aged 74 following an eight-month battle with lung cancer and after previously describing how some people they knew had crossed the street to avoid awkward conversations.
He's now admitted there is no way he will be letting them back into his life.
"I'm very unequivocal, black and white, all or nothing," he told the Sunday Times magazine.
"I've tried to go for the grey areas but it's not succeeded for very long. There are people that have been edited out of my life and I will never see them again, he said.
"If I had done that to them, I wouldn't be able to look them in the face."
Pressed on if he could forgive them if he knew they had good intentions, he added: "No, portcullis down. Goodbye."
The 69-year-old star now "lives in a commune" after daughter Olivia and her husband Florian Herbst - who recently became parents for the first time - asked if they "could come back" following a few years living separately, having previously all shared space during the COVID-19 pandemic.
"They asked if they could come back. So now I live in a commune," he said.
Within his "interdependent father-daughter relationship", Grant has found "incredible" joy in the first four weeks of being a grandfather.
"Seeing your child become the parent of their child is … how do you quantify that? It is the most fulfilling thing to seem," he said.
He admitted becoming a grandparent has made him think more of his own mortality, but he views it as a positive.
"What everybody will tell you about becoming a grandparent is that the parents do all the nappy changing, feeding, they do all that. I'm spared having to be up all night, which I would love. I'm just handed the baby. I get the best of it.
"I've felt that overwhelming thing that you're part of the cycle of life. You've gone through death and now there's a birth. I instantly thought, how many Christmases will I have to share with the grandchild? That's the thing that galvanises you - how many years of life you have left.
"I'm 69 - the oldest man in show business - so I'm hoping for another 31 years, but the likelihood of that is slim...
"A grandchild underlines your own mortality but that's a good thing because you don't waste time on stuff. You have a finite amount of time ahead of you."
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