LONDON — Surely the filament-thin and translucently pale girl in the water couldn’t keep it up. Fifteen-year-old Katie Ledecky was so far out in front in the Olympic 800 meters that she was swimming alone. “I didn’t see a lot of splashing,” she said. You waited, along with her rivals, for her to fade and the record pace to turn out to be just a flirtation. Surely the child would tire.

“I just didn’t want to die and fall back,” she said,

There were two people in the Aquatic Centre who knew she wouldn’t, that this slight, auburn-haired progeny from Bethesda, with her inside-the-beltway skybox connections, had iron in her. With 200 meters still to go, Dave and Mary Gen Ledecky turned to each other and embraced. A quarter of the race remained, but as far as Ledecky’s parents were concerned, it was over. They understood what others would hardly suspect, from opponents to schoolgirl friends at the Stone Ridge School of the Sacred Heart.

“If you see her on the street or sit with her at lunch, you wouldn’t know she can close on you like that,” Mary Gen said.

In the end Ledecky yielded a world record by a fraction, merely breaking the American mark for the 800 meters. When it was over, the youngest member of the U.S. swim team did with her gold medal what any 15-year-old does with a valuable piece of jewelry she has been given but is not yet old enough to wear. She gave it to her mother for safekeeping.

“Let me see it,” Mary Gen said.

“That’s a big honkin’ gold medal,” Dave said.

Less than a day later, Ledecky’s parents sat in the bar of a hotel on the Thames riverbank with a plate-glass view of Parliament’s Big Ben clock tower behind them, still exhilarated with their daughter’s achievement and squint-eyed with lack of sleep. She had just won what was arguably the most astounding medal of the entire London Games, one so unforeseen on the international stage that it led to the following exchanges in her post-race press conference.

Question: “What grade will you be in this fall?”

Answer: “Sophomore.”

Question: “You’re very young. Are you surprised . . . ?”

Answer: “I didn’t really expect gold but, ummm. I’ll take it.”

Ledecky’s arrival on the international stage is so premature that as recently as September she wasn’t even thinking about swimming in London, let alone winning a medal, she said. Her coach, Yuri Suguiyama, sat her down for a conversation at the beginning of the fall season.

“Now Katie, what would be the ultimate goal?” he asked.

“I dunno,” she replied.

“Maybe the Olympics?” he suggested.

“Yeah,” she said.

He made her say it aloud — with conviction. The he asked her to repeat it. Afterwards she went home and repeated her new ambition to her mother. “But I don’t want to tell anyone,” she said uncertainly. Mary Gen replied, “Then don’t talk to me about it.”

The rest of the Ledecky family fully expected Katie to compete for a medal in London. Two years ago her uncle, Jon Ledecky, told his friend and one-time partner Ted Leonsis to “watch out for Katie and her upside in the pool.”

“Jon told me she was ‘clutch’ and a ‘closer,’ ” Leonsis wrote in response to an e-mail query.

It’s hard to find a family more enmeshed in competitive Washington power circles than the Ledeckys, though quietly so. Dave was an attorney for many years at Kirkland & Ellis before taking the past year off to devote it to his daughter’s swimming. Mary Gen is a former associate administrator of Georgetown Hospital. Jon Ledecky partnered with his good friend Leonsis in purchasing a stake in the Capitals and Wizards in 1999. “Katie’s family is filled with high achievers,” Leonsis reports. “Uber smart — hyper competitive.”

Katie was a fixture in the owners’ box at what is now Verizon Center. Leonsis recalls her at age 2, sitting next to Michael Jordan and coloring obliviously in her coloring book on the night Jordan was announced as a co-owner of the Wizards. With her brother Michael, she went to “hundreds” of Caps games, knew every player and all of their stats. She wore a Caps jersey and flung herself at the mascot Slapshot for hugs.

She absorbed competitiveness by osmosis, though it may also run in the family genetically. Her maternal grandfather, Edward J. Hagan, won a Silver Star and two Bronze Stars serving as a combat surgeon in the South Pacific in World War II. Then he came home to Williston, N.D., where as chairman of the city park board he built a municipal swimming pool, which is now named after him. Mary Gen (short for Genevieve) was ranked in the national top 20 in the 200 freestyle as a swimmer at the University of New Mexico.

But to some, Ledecky’s metamorphosis from schoolgirl to Olympic champion is less than natural. The 800 is the longest race for women, and teenagers simply don’t swim it like this — not unless their name is Janet Evans. Most of them wilt. Yet at the U.S. trials last month Ledecky knocked more than five seconds off her personal best, and she shaved another five seconds off it on Friday to win gold. When China’s Ye Shiwen showed such a dramatic leap in the 400 earlier in the week, observers, including an American coach, questioned whether she was doping.

It was inevitable that the same question would be asked of Ledecky. What did she say to those who believe she must have doped?

“That’s totally false,” she said calmly.

It wasn’t the first time the Ledeckys have heard questions about Katie’s methods. For the past year as her times fell other parents have quizzed them about how she was doing it. One asked Mary Gen, “What is she eating?”

Their reply is that their daughter doesn’t put a morsel in her system without checking the contents. “She won’t even take a multivitamin,” her mother said. If equanimity is proof, Ledecky is innocent. The discussion doesn’t seem to perturb the swimmer, or her family. “The only thing she will test positive for is hard work,” her father said. Mary Gen added, “We don’t care if people say it. It doesn’t bother her.”

The Ledeckys experienced just one brief moment of doubt regarding their daughter in London. It came when they climbed to their seats in the bleachers just before the race. Dave asked his wife, “What are we going to say to her if she doesn’t make the medal stand?” They considered for a moment. “It wasn’t that I didn’t believe in her, but I just wanted to handle it right,” he says. They agreed they would tell her she’d had a wonderful adventure and it was time to get back home, and back to work.

A minute later they decided their seats were too high up, and they walked back down to a handicapped section just above the pool deck, where a couple friendly ushers let them loiter. They shrank back in a corner so Katie wouldn’t see them when she walked across the deck to her starting block. “I didn’t want to freak her out,” Mary Gen said.

Minutes later, the roars reverberated off the walls. With 150 meters to go, the Ledeckys broke their hug and began clapping each other on the shoulders with excitement. Their daughter’s stroke was strong and undiminished as she finished out. She was the only one in the arena who didn’t know she’d won.

“I didn’t know I’d won until the 799-meter mark,” she said. “I knew I was winning but I didn’t put it out of the question that someone could come from behind or touch me out.”

The next several hours were tumultuous: press conferences, interviews with NBC and an exhausted 3 a.m. toast at their hotel. When they finally went to bed, they did so with a sense of unreality. Jon teased Dave that he would sleep with the medal “under his pillow.” When they awoke on Saturday morning they half-expected to discover that none of it really happened. “I thought the medal might be gone,” Dave said. But it was real.

“I checked again an hour ago,” Dave said. “It was still there.”

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