ARLINGTON, Virginia (AP) -- George Washington's adopted son was a bit of a ne’er-do-well by most accounts, including those of Washington himself, who wrote about his frustrations with the boy they called “Wash.”

“From his infancy, I have discovered an almost unconquerable disposition to indolence in everything that did not tend to his amusements,” the founding father wrote.

At the time, George Washington Parke Custis was 16 and attending Princeton, one of several schools he bounced in and out of. Before long, he was back home at Mount Vernon, where he would be accused of fathering children with slaves.

Two centuries later, the National Park Service and the nonprofit that runs Washington's Mount Vernon estate are concluding that the rumors were true: In separate exhibits, they show that the first family’s family tree has been biracial from its earliest branches.

“There is no more pushing this history to the side,” said Matthew Penrod, a National Park Service ranger and programs manager at Arlington House, where the lives of the Washingtons, their slaves and Confederate Gen. Robert E. Lee all converged.

President George Washington had no direct descendants, and his wife Martha Custis was a widow when they married, but he adopted Martha‘s grandchildren – “Wash” and his sister “Nellie” -- and raised them on his Mount Vernon estate.

Parke Custis married Mary Fitzhugh in 1804, and they had one daughter who survived into adulthood, Mary Anna Randolph Custis. In 1831, she married her third cousin -- Lee, who then served as a US Army lieutenant.

Outside the marriage, Parke Custis likely fathered children with two of his stepfather’s slaves: Arianna Carter, and Caroline Branham, according to the exhibits at Arlington House and Mount Vernon.

The first official acknowledgment came in June when the Park Service re-enacted the 1821 wedding of Maria Carter to Charles Syphax at Arlington House, the hilltop mansion overlooking the capital that Custis built (and Lee later managed) as a shrine to his adoptive stepfather. A new family tree, unveiled at the re-enactment, lists the bride's parents as Parke Custis and Arianna Carter.

“We fully recognize that the first family of this country was much more than what it appeared on the surface” Penrod said at the ceremony.

The privately run Mount Vernon estate explores this slave history in “Lives Bound Together,” an exhibition opening this year that acknowledges that Parke Custis also likely fathered a girl named Lucy with slave Caroline Branham.

Tour guides were hardly this frank when Penrod started at Arlington House 26 years ago. Staffers were told to describe slave dwellings as “servants’ quarters,” and “the focus was on Lee, to honor him and show him in the most positive light,” Penrod said.

He said no new, definitive evidence has surfaced to prove Parke Custis fathered girls with slaves; rather, the recognition reflects a growing sense that African-American history cannot be disregarded and that Arlington House represents more than Lee's legacy, he said.

Scientific proof would require matching the DNA of Carter and Branham descendants to the progeny of his daughter and the Confederate general, because the Parke Custis line runs exclusively through the offspring of his daughter and Robert E. Lee.

Stephen Hammond of Reston, a Syphax descendant, has researched his family tree extensively. He said the Park Service’s recognition of the Custis' paternity is gratifying. “It’s become a passion of mine, figuring out where we fit in American history,” Hammond said.

Hammond said he and his cousins have yet to approach the Lee descendants to gauge their interest in genetic tests, and it's not clear how they feel about the official recognition -- several didn’t respond to Associated Press requests for comment.

Some family records are kept at Robert E. Lee‘s birthplace, Stratford Hall, but research director Judy Hynson said she knows of none that acknowledge Parke Custis fathered slaves.

“That’s not something you would write down in your family Bible,” Hynson said.

The circumstantial evidence includes the Carter-Syphax wedding in Arlington House -- an unusual honor for slaves -- and the fact that Parke Custis not only freed Maria Syphax and her sons before the Civil War, but set aside 17 acres on the estate for her.

Indeed, after Arlington House was seized by Union forces, an act of Congress ensured that land was returned to Maria Syphax's family. New York Sen. Ira Harris said then that Washington’s adopted son had a special interest in her – “something perhaps akin to a paternal instinct.”

Oral histories also argue for shared bloodlines.

Maria Carter's descendants know, for example, that her name was pronounced “Ma-RYE-eh,” not “Ma-REE-uh,” said Donna Kunkel of Los Angeles, who portrayed her ancestor at the re-enactment.

“As a kid I would always tell people I was related to George Washington, but no one would believe me,” she said.

Branham descendants include ZSun-nee Miller-Matema of Hagerstown, Md., who said “my aunt told me that if the truth of our family was known, it would topple the first families of Virginia.”

She said she discovered her truth by happenstance in the 1990s, when she spotted a portrait with a family resemblance while researching at the Alexandria Black History Museum for a stage production. A museum staffer soon sat her down with records. Eventually, she traced her ancestry to Caroline Branham, who appears in documents written in the first president’s own hand.

“I just couldn't believe it,” she said. “Gen. Washington was taking notes on my Caroline?”

As slaves, the women could not consent to the sexual advances of the plantation owner’s adopted son, but Kunkel said she tries not to think of the acts as rape.

“I try to focus on the outcome. He treated Maria with respect after the fact,” she said.

Incorporating these family histories into the nation's shared story is particularly important at a time of renewed racial tension, Miller-Matema said.

“We’re all so much a part of each other,” she said. “It just makes no sense any more to be a house divided.”