Like many of the nation’s founding fathers, George Washington had a complicated relationship with slavery. At the tender age of 11, he inherited 10 enslaved workers along with 280 acres of land, upon his father’s death. His personal wealth—including enslaved workers—increased dramatically when he married Martha Dandridge Custis, the young widow of a wealthy planter, in 1759. (The couple had no children together; some have speculated that Martha had been injured in the birth of her youngest child, and couldn’t have more children, or that an early bout of smallpox left Washington sterile.)

As a young man, Washington was known as a harsh master, but later accounts suggest he treated them more humanely by the standard of other Virginia planters. During the Revolutionary War, the colonial struggle for freedom from Britain clearly altered Washington’s attitude toward slavery. “The unfortunate condition of the persons, whose labour in part I employed, has been the only unavoidable subject of regret,” he wrote late in his life. In his will, Washington made provisions to set 100 slaves free after his wife’s death. Even so, nearly 200 enslaved people remained at Mount Vernon, under the ownership of George Washington Parke Custis and his sister, Eleanor Parke Custis Lewis, whom Washington had adopted and raised as his own.

The acknowledgement of Washington’s biracial family tree by the National Park Service and the nonprofit that runs the Mount Vernon estate is the latest development in more than 200 years of speculation about the complicated history of the nation’s “first family.” The first step of this historic recognition came in June, when the Park Service held a reenactment of the marriage of Maria (pronounced “Ma-RYE-eh”) Carter to Charles Syphax at Arlington House, the hilltop mansion built by Parke Custis and later managed by his son-in-law, Robert E. Lee. Both Carter and Syphax were enslaved workers at Mount Vernon, working as household servants, when they married in 1821. A new family tree unveiled at the reenactment listed George Washington Parke Custis and Arianna Carter as the bride’s parents.

“We fully recognize that the first family of this country was much more than what it appeared on the surface,” Matthew Penrod, a National Park Service ranger and programs manager at Arlington House, said at the ceremony. In addition to the reenactment, a new exhibit opening at Arlington House this year, “Lives Bound Together,” acknowledges that in addition to Maria Carter, Parke Custis likely also had a daughter, Lucy, with Caroline Branham, another of Washington’s enslaved workers.

While no new, definitive evidence has surfaced to prove Parke Custis fathered the two girls with Carter and Branham, rumors to that effect have long existed underneath the more widely known history of the nation’s first family. Circumstantial evidence to support his paternity, in the case of Maria Carter, includes the fact that her marriage to Charles Syphax was held at Arlington House, which would have been a rare honor for enslaved workers. There’s also the fact that Parke Custis freed Maria Syphax and her sons in 1826, setting aside 17 acres on the estate for her to live on.

After Union forces seized Mount Vernon during the Civil War, an act of Congress returned the land to Carter based on her more than 30 years of occupancy. At the time, New York Senator Ira Harris said that Parke Custis had a special interest in Maria Syphax, describing his feeling towards her as “something perhaps akin to a paternal instinct.” The Syphaxes had 10 children who lived free on the estate; their eldest son, John Syphax, was educated in Washington, D.C. schools and became a property owner in his own right, serving in several elective offices. His brother, William Syphax, served as chief messenger of the Department of the Interior, and led efforts to establish public high school education for African Americans in the D.C. school system.

Oral traditions in both the Carter-Syphax and Branham families also recorded the shared bloodline. Syphax family tradition always held that Parke Custis was Maria Carter’s father, while ZSun-nee Miller-Matema, a Branham descendant, told the Associated Press that “My aunt told me that if the truth of our family was known, it would topple the first families of Virginia.” Miller-Matema herself discovered her link to Washington when doing research in the 1990s at the Alexandria Black History Museum. After tracing her ancestry back to Caroline Branham, she found her ancestor’s name in documents written in the founding father’s own hand.

According to Penrod, his organization’s official acknowledgement of Washington’s biracial family tree is a nod to the growing sense of the importance of honoring African-American history, as well as the complicated legacy of Arlington House. “There is no more pushing this history to the side,” he told the AP of the new exhibits. Miller-Matema, Branham’s descendant, believes the shared history is especially important to acknowledge in a time of continuing racial tensions: “We’re all so much a part of each other. It just makes no sense any more to be a house divided.”

As the Parke Custis line runs only through the descendants of his daughter and Robert E. Lee, obtaining scientific proof of the shared bloodline would require comparing the DNA of Carter and Branham descendants with those of Mary Custis Lee and the Confederate general. So far, it is unclear whether or not Lee’s descendants would agree to such testing. While some family records are kept at Robert E. Lee’s birthplace, Stratford Hall, none are known to refer to the fact that Parke Custis fathered children with enslaved women.