HOUSTON -- "When I found out, I started to get a little bit nervous."
Michael O'Mara always knew his family had a copy of the Declaration of Independence, but he thought it was nothing special.
"Growing up around these things, it just wasn't that big of a deal," O'Mara said.
The document was part of a few heirlooms passed down that are believed to have belonged to President James Madison, who is O'Mara's fifth great uncle.
The copy was hidden away in the 1800's, eventually making it to a Kentucky closet in the '60s, before ending up in Houston-unseen for 10 years.
"I left it there in my office because I knew it was safe there," O'Mara said.
He says this pocket watch and decanter, which he keeps in a safety deposit box, also belonged to Madison, but it was the value of the document that surprised him.
"Been in my immediate family since the 1960's. I always knew what they were and their heritage, but at that point in time, they didn't have a lot of value."
He sent it off to the National Archives to be restored.
Experts are aware of only about 50 reported similar copies remaining.
O'Mara just sold the copy to a buyer in New York City for an undisclosed amount. There are plans in place for it to be displayed first at the Smithsonian and eventually at a more permanent home.
NATIONAL TREASURE: Man sells rare copy of Declaration of Independence
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