Jimmy Carter and Wife Rosalynn Are Planning 75th Anniversary Party This Summer: 'Incredible Milestone'

When they reach 75 years of marriage together this summer, Jimmy and Rosalynn Carter want to celebrate their "incredible milestone" in a big way, grandson Jason Carter says.

"What they're really doing these days is planning their 75th anniversary party for July," Jason, who appears in a new documentary about his grandfather, tells PEOPLE of the longest-married presidential couple in U.S. history.

While the former president and first lady have been keeping a lower profile amid the COVID-19 pandemic, they resumed some public appearances earlier this year after being fully vaccinated.

Jason, 45, says the plan in July is for a private event that he says should be a "big party ... with a lot of their friends from over the years."

The bash for Mrs. Carter, 93, and her first and only love, now 96, will be held in their hometown of Plains, Georgia — not at the Carters' modest ranch home but "at different sorts of locations," Jason says.

"The number of things that have to go right in your life to have a 75th anniversary," he says, "it's a truly incredible milestone."

President Carter has been no less effusive.

"The best thing I ever did was marrying Rosalynn," he said during a 2015 interview at The Carter Center, their humanitarian organization. "That's the pinnacle of my life."

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Universal History Archive/Getty From left: President Jimmy Carter and First Lady Rosalynn Carter dancing at a White House congressional ball in 1977.

Matt McClain/The Washington Post/Getty From left: former President Jimmy Carter and former First Lady Rosalynn Carter walk toward their home in Plains, Georgia, following dinner at a friend's home on Aug. 4, 2018.

Looking Back at Their Love Story

Rosalynn Smith and Jimmy Carter wed on July 7, 1946, at a Methodist church in Plains. Carter was 21 and Rosalynn was 19, and the ceremony was held following his graduation from the U.S. Naval Academy.

The couple had known each other most of their lives: Jimmy's sister Ruth Carter was Rosalynn's best friend since childhood, Rosalynn recalled in Phil Donahue and Marlo Thomas' What Makes a Marriage Last, published last year.

"I first started noticing him when I was thirteen," she said in the book, "and, I mean, there's just no relationship between a thirteen-year-old and a sixteen-year-old in that situation."

But by the time she was 18, Rosalynn was ready to pursue Jimmy when he returned to Georgia on a month-long break from the Naval Academy in Annapolis, Maryland.

"Ruth and I plotted to get me together with him. She'd call and say 'Come over! He's here!' and I'd go flying over to her house, but he'd be gone again," she said in What Makes a Marriage Last.

"I always said I fell in love with a photograph of him on her [Ruth's] bedroom wall," Rosalynn said.

She said that "I didn't know a single boy I thought I'd want to spend my life with" — until Jimmy came calling.

Rick Diamond/Getty From left: Rosalynn and Jimmy Carter attend a fundraiser on Valentine's Day in 1976.

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On the last night of one of his breaks from the Naval Academy, fate would have it that he found himself without a date while his then-girlfriend was at a family reunion at which he was not allowed.

"I was cruising around with my sister Ruth and her boyfriend, just looking for a date, and I picked up Rosalynn in front of the Methodist church," he said in What Makes a Marriage Last. He invited her to the movies.

"I just felt compatible with her," he said. "She was beautiful and innocent, and there was a resonance. We rode in the rumble seat of a Ford pickup—Ruth and her boyfriend in the front—and I kissed her on that first date. I remember that vividly."

The next morning, he told his mother that "Rosalynn was the one I wanted to marry."

Bettmann/Getty President Jimmy Carter (center) carries his grandson Jason on his shoulders as he mingles on the South Lawn of the White House during the annual Easter Egg Roll. With them are Amy Carter and First Lady Rosalynn Carter.

The Carters went on to have four children — sons Jack, Chip and Jeff and, after a 14-year gap, daughter Amy, who spent part of her childhood in the White House.

The couple have since attributed their marriage's longevity to a mix of shared hobbies, including bird-watching ("Rosa and I have seen about 1,300 different species of bird"), mutual support and their faith. Each night they still read the Bible together.

"I think the best explanation for that is to marry the best spouse," President Carter told PEOPLE in 2019 of his continued zeal, "someone who will take care of you and engage and do things to challenge you and keep you alive and interested in life."