Edoardo Mapelli Mozzi does not speak to his son's grandmother, Lily Huang, who has revealed the information in a rare interview.
Lily's daughter, Dara Huang, dated Mr Mapelli Mozzi between 2015 and 2018, and welcomed a son named Christopher Woolf (Wolfie) in 2016.
Mr Mapelli Mozzi went on to marry Princess Beatrice in 2020, with whom he shares two daughters, Sienna, four, and Athena, one.
Lily has now revealed that her daughter's ex-boyfriend is not on speaking terms with Dara's parents.
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She told the Mail that she and her husband, Po-Tien, "never see Edo".
Lily added: "Why should we see him or speak with him?"
However, Wolfie's grandmother clarified that she does occasionally see Princess Beatrice on the news.
She explained: "We are both very old, and my husband is sick. I never ask Wolfie about his stepmother, but I see her on the television."
Edoardo Mapelli Mozzi does not speak to son's grandmother as family split revealed
|GETTY / INSTAGRAM: DARA HUANG
Dara previously spoke out about her ex-boyfriend and whether she loved him, telling Lifestyle Asia: "He was the father of my child, and he left as quickly as he came, so I would say unfortunately it's not an instinct you can trust!"
Po-Tien, a retired scientist with the US space agency Nasa, spoke to the Mail in December 2018 after it was confirmed that Mr Mapelli Mozzi had begun dating Beatrice.
At the time, he said: "Why would they want to go and break this up? I can’t understand it. It’s not fair, but the Royal Family are so powerful. What can I do? I can’t do anything.
"Dara came back here from London for Thanksgiving with Wolfie. She didn’t know anything about it, and the next day her friend emailed the newspaper report to her.
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Wolfie Mapelli Mozzi pictured with his maternal grandfather, Po-Tien Huang
|INSTAGRAM: DARA HUANG
"She showed me and her mum and then we knew what was going on. It’s a sad time and sad situation. We don’t know how Dara is going to take care of it. I’m upset, but there’s nothing I can do about it.
"Being angry is no solution. These things happen in all the world – today it happened in my home.
"No matter what we say, it doesn’t help, so let him go."
Po-Tien added: "Edo came for Christmas here last year, and we have travelled to England to meet Edo’s family. I asked Edo and Dara when they were going to get married.
Lily Huang with her daughter, Dara Huang, who splits her time between London and Florida
|INSTAGRAM: DARA HUANG
"I even emailed Edo about it, but they said they didn’t want to rush. Everything was pretty and so nice until this happened."
A Palace aide defended Beatrice against these reports at the time, telling the Mail: "She [Beatrice] would never allow herself to break into another couple’s happiness, especially if there was a small child."
Meanwhile, a friend of Mr Mapelli Mozzi Mozzi said: "As always in these cases, there are two sides to the story."