Bryan Kehl leans back, smiles and says his dad has always been a "storyteller."

He wraps exaggerated finger quotes around that last word to make it clear the stories his father tells aren't always rigorously fact-checked.

Six of Gary and Nancy Kehl's nine children were adopted, including Bryan. As a rule, there were never any distinctions made about whose genes came from where: Everyone was to be treated equally. But there was always one exception—and it always involved Bryan.

Giants linebacker Bryan Kehl, above after a preseason win against the Patriots, was adopted. He didn't find out until last year that his father was NFL journeyman running back Maurice Turner. Emile Wamsteker for The Wall Street Journal

In one of those yarns that his dad was so fond of telling, Bryan's biological father was an NFL running back. "I wasn't sure it was true," he says. "Like I said, my dad tells stories.''

The first time Bryan touched a football, however, out in the family's backyard in Salt Lake City, he decided to play running back. All through youth football and until he went to high school, he was a running back. Now, some 20 years after that first run, he thinks his fondness for carrying the ball was influenced by family lore. "I'm sure that had something to do with it. My brothers all played defense."

Mr. Kehl is a strapping 26-year-old linebacker entering his third season for the New York Giants. He's no longer a running back. He plays defense like the rest of the Kehls.

But when it comes to his path to the NFL, there's something basic that Bryan Kehl doesn't know—whether his athletic talent was something bred into him by his parents, his siblings and his Utah childhood, or whether it was coded into his DNA.

Kehl with his adoptive parents Gary and Nancy, and his wife Jessica. Emile Wamsteker for The Wall Street Journal

Unlike most people, whose sense of their origins grows deeper as the years go by, Bryan Kehl's has moved in the opposite direction. The mystery of who he is, and exactly how he got there, is still a deep one.

Nancy Kehl had three children when she decided she wanted a fourth—a half-white, half-black baby girl the Church of Jesus Christ of Latter-day Saints' adoption program couldn't place.

Mrs. Kehl says she found out soon after the adoption why that might have been the case: Her neighbors told her that her children could no longer come over. Still, four years later, there were three more biracial Kehls: Bryan, Kortney and Ed. The first three arrived as infants while Ed came as a 12-year-old.

Bryan Kehl with his biological father Maurice Turner. Kehl Family

The Kehls were a rambunctious and athletic lot, but Bryan's supposedly special "background" still earned notice. There were times when Bryan would juke a defender or make a great run and the neighborhood kids would say: "Yeah, his birth dad's an NFL player."

The years passed. Bryan never searched any NFL rosters. He didn't go look at old college media guides, either. To him, it was just a story. And besides, he knew who his parents were.

Meanwhile, up in the St. Paul, Minn., suburb of Shoreview, Maurice Turner would catch a college football game, hear the surname "Turner" and stop for a second, wondering if that was his son, the child his long-ago girlfriend Amy had put up for adoption. His other two sons, with wife Keren, played football.

"I knew that the child's name wouldn't be Turner, but the thought runs through your mind," he said.

Keren hadn't dated Mr. Turner for two weeks before he told her that he had a son. That son's birth date was etched first in Mr. Turner's dog-eared Bible, above where his marriage to Keren and the birth dates of their other children, Maurice Jr. and Billy, eventually went. "Our boys never felt cheated," Mrs. Turner says. "It was just something we all always knew—that one day we would find him and our family would be complete."

The Turners searched for the baby over the years, even calling the LDS church. But Mr. Turner never knew where the child was born and he couldn't get comfortable with broaching the one tenuous connection he had: As college students at Utah State, he and Amy had set up one of his friends with one of hers and that couple had married.

Amy—now Amy Smith—was in Utah, too, and raising five kids with her husband, Brian.

She had once loved Mr. Turner. She had ignored that he was black and Catholic and that she was white and Mormon, even as her parents pulled her out of Utah State because they couldn't ignore it. She cajoled her way back to campus, where she and Mr. Turner reunited. Later, he graduated and she found out she was pregnant. She thought they would get married; he said it wouldn't work. She said she would put the baby up for adoption. He begged her not to, pleading that he would raise the child.

"I didn't like that idea, either. I felt the baby deserved a family, to have a mom and dad that were stable," Mrs. Smith says. Then, more quietly: "Twenty-five years later, I have found out how much that affected him. I really didn't think he cared that much."

Bryan Kehl certainly didn't care. Not at BYU, not on his LDS mission in Toronto and not even when he was drafted in 2008. Then a Giants physical found he had a sickle-cell trait, and head trainer Ronnie Barnes asked for a family medical history. "I had no idea," he remembers.

Turns out Mr. Barnes was adopted, too, and Mr. Kehl felt a seed of curiosity. That seed sprouted last fall, when on a random November night he decided to see if a 1983 draft list lived on the Internet.

There it was, in the 12th round to the Vikings, a running back from Utah State named Maurice Turner.

Mr. Turner, who had spent five years bouncing around the NFL, was listed at 5-foot-11 and 200 pounds. In high school, Mr. Kehl had found an old form in a filing cabinet listing his birth parents' races, ages and personal traits. The mother was smart and good-looking. The father was gregarious, 6-feet-tall and weighed 200 pounds. "Honestly, I still thought it was a coincidence," he says.

Still, he casually mentioned it to his mother at Thanksgiving. The next week, while in California, Mrs. Kehl told her girlfriends and suddenly these Utah housewives had a case to crack. One friend started Googling Mr. Turner, another found a number and Mrs. Kehl dialed it.

Is this Maurice Turner? Did you play football at Utah State? Did you give up a child for adoption 25 years ago?

"He said, 'I have waited 25-plus years for this phone call,' " Mrs. Kehl remembers. "He was so humble, so sweet. He was awesome. But why wouldn't he be? Bryan is, too."

She gave him her son's number—their son's number—and minutes later, on Dec. 3, Mr. Turner and Mr. Kehl started what would become a two-hour conversation. They talked about life, family and faith with voices that sounded eerily similar. Mr. Turner cried. Their wives emailed pictures as they talked and the two men knew: This was real. "He right away let me know that he felt he had a great life, that he had been loved, that he had been very well taken care of. There's a sense of relief that he had not been abused," Mr. Turner said. "At the same time, there's a sense of anger: Those same things, I could've given him."

As Bryan and Maurice talked, Mrs. Kehl put off telling her husband, calling various children first. Until she called Ed, who, ever-conscious of their dad's feelings, scolded her.

"I was blindsided," Gary Kehl says. But with a cheer his children say is characteristic, he adds, "That's my wife, full-steam ahead."

As fate had it, the Giants closed their season at the Vikings on Jan. 3. The Kehls flew out from Utah, the Turners met them in the team's Minneapolis hotel and Bryan's wife, Jessica, said hugging Mr. Turner "felt familiar."

Surreal, awe-inspiring, indescribable—the Kehls and Turners run through a litany of adjectives trying to explain that first meeting. "You don't want this person to have a negative impact on your son because you've worked so hard to raise him this way," Gary Kehl says. "That was solved as soon as we met him. I started telling him about Bryan, he got emotional and I knew then. I put my arm around him and I said, 'Hey, I understand.' "

The Giants wrapped up their ignominious season in Minnesota and a few days later, Bryan and Jessica flew to Utah. In mid-December, Mr. Kehl had reached Amy Smith through the wife of that old friend of Mr. Turner's, and now he wanted to meet her, too. "If it's sitting right there, you want to know," he says.

The easy familiarity took longer with Mrs. Smith. She'd never considered that the baby would find her, and she still harbored shame from the out-of-wedlock pregnancy all those years before. She prayed and she worried, and it took one stilted meeting, one better lunch and six weeks before she told her kids.

She invited Bryan and Jessica to her home, she called her parents and six siblings and the ice officially broke when her 11-year-old son, Max, not realizing Mr. Kehl is biracial, said, "Wow, he's been in the sun."

One of her sisters bawled when she saw him, her father kissed him and Amy's brother John, a monstrous BYU fan, insisted he'd always felt some sort of inexplicable affinity for Mr. Kehl. "Everything about this story is crazy," Mr. Kehl says.

Crazy and inspiring and wrenching, too, Mrs. Smith says.

"Maurice had been praying for this for 25 years. I hadn't," she says. She uses the words "grateful" and "blessed" to describe meeting Mr. Kehl, and she expresses happiness that he is in her life. But she also says she felt more in control before, and this "is a little tricky."

There's no guidebook on how any of this works. Mrs. Smith doesn't know how often to call. Mr. Turner can't call enough. Mr. Turner always said he had three sons. Mrs. Smith is bothered when someone refers to Mr. Kehl as her son. "That's for who raises you," she says.

So what about the old "story" Gary Kehl used to tell his son that his birth father was an NFL running back?

Mr. Kehl says he remembers someone at the adoption agency telling him that, although he can't remember the details and never saw any paperwork. His wife, Nancy, still suspects that her husband made the whole story up.

Either way for Bryan Kehl, whether the story is true or not and whether he owes his talent to nature or nurture, it's all the same. "I went to two parents who love me and were the best parents that a kid could ever have and I was born to two parents who are awesome parents," he says. "I know I'm lucky. This could be a very different story."

Write to Aditi Kinkhabwala at aditi.kinkhabwala@wsj.com