The prime minister reportedly told his father, a former member of the European Parliament (MEP), is was “magnifique" that he had secured French nationality on Wednesday, after he applied in November 2021.
France’s justice ministry said the decision "only regards Mr Stanley Johnson and does not extend to his descendants”.
Mr Johnson, 81, voted to remain in the EU in the 2016 referendum in opposition to his son who was a figurehead for Vote Leave and ultimately led Britain out of the bloc at the end of 2020.
Speaking to the PA news agency, Stanley Johnson said: “I’m absolutely delighted and have no idea at what level this decision was taken but I do think it was a very imaginative thing to do at this moment, at a time when (UK) relations with France and the EU are not necessarily the best. I think it’s very nice for arms to be stretched out one way or another.
“I got a one word reply from Boris, which said, ‘Magnifique’.”
Stanley Johnson said the “most significant reason was really sentimental”, with his mother Irene Williams having been born in Versailles.
But, he added: “It was a little gesture of saying that although the UK may have left the EU we haven’t actually left Europe.
“It’s a tiny gesture on my part that I certainly don’t regard ourselves as being cast aside from Europe and I would say realistically as we look ahead and try to solve these trade issues, the only way we’re going to solve them is to retain a degree of commonality in our two systems.“
Asked how it is to be a citizen of the EU once again, he replied “Pourquoi pas? J’en suis tres fier”, or “why not, I’m very proud of it”.
Stanley Johnson was one of the first civil servants from the UK to work in Brussels after the UK joined the bloc in 1973.
He joked: “Maybe I could stand for the European Parliament again for a French constituency.”
No 10 declined to discuss Mr Johnson’s new citizenship, saying it is “a personal matter for the prime minister’s father”.
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