Lord Ivar Mountbatten will marry his partner James Coyle this summer.
In doing so, Mountbatten, the third cousin once removed of Queen Elizabeth, will become the first member of the extended British royal family to enter into a same-sex marriage.
In a family interview with Daily Mail, Coyle, 56, called their union "a very modern marriage" and "there was no proposal, just an acceptance of this great love."
Mountbatten, 55, was previously married to Penelope Thompson. The pair divorced in 2011 after having three children: Ella, Alexandra, and Louise. He came out in 2016.
In a modern twist, Thompson will give away her ex-husband at the ceremony, which will take place in a private chapel at Mountbatten's estate in Devon. The idea came from their daughters.
"It makes me feel quite emotional. I'm really very touched," said Thompson, who observed that her husband has never looked happier since coming out.
Mountbatten said that, while he previously thought he would not marry again, he "really wanted to do it for James."
"James hasn't had the stable life I have," he said. Mountbatten, speaking to Coyle, said, "I want to be able to give you that."
"I never thought this would happen. It's brilliant, but I never thought I'd marry a man," Mountbatten said. He recalled that, when he was growing up, "gay men were called poofs, queers, everything derogatory under the sun."
"In 15, 20 years' time, people will struggle to understand how we came to be having such conversations," he said. "People will look back and say, 'What's the big deal?' But for our generation it was."