Richard Nixon hid one unlikely item in his Oval Office desk

While Richard Nixon always kept a yellow writing pad full of scribbles in hand, one of his most valuable possessions was actually secretly tucked away in his Oval Office desk.

SEE ALSO: Eyebrow-raising donation revealed in Clinton emails

"My grandfather kept a little card that listed his 10 different rules for being president," his grandson, Christopher Nixon Cox, revealed in an exclusive interview with AOL.

Nixon Cox found the little-known keepsake when his grandfather died in 1994 -- and he even revealed one of the rules that stuck with him: "Don't forget you should always have a way out of an issue."

He gathered with several members of his family on Friday to celebrate the grand re-opening of the Richard Nixon Library and Museum in Yorba Linda, Calif., the former president's birthplace. Other important politicians, such as former Secretary of State Henry Kissinger and former California Gov. Pete Wilson, were also in attendance.

The $15 million project includes an exact replica of the 37th president's Oval Office. It was designed in the original 1969 décor of California blue and gold, which was hand selected by first lady Pat Nixon.

The new space also features more than 300 artifacts, including the original revolver rock icon Elvis Presley gave Nixon during his impromptu visit to the White House in 1970. A photo featuring the two prominent figures shaking hands in the Oval Office is the most requested photo in the National Archives to this day.

Dr. Henry Kissinger, the former president's secretary of state, gave the keynote speech at the event.

"He had the courage and the vision to open to China and to put before the American people a new vision of world order," Kissinger said, praising his close friend.

He aided Nixon in his historic visit to China in 1972, which marked the first time a U.S. president set foot on Chinese soil.

"For once a White House public relations strategy succeeded, and performed a diplomatic function as well," Kissinger wrote in his 1979 book, "White House Years."

And though the new Richard Nixon Library and Museum gave visitors an up close and personal look into the life of the 37th president, his grandson did confess one cute item he kept in the Oval Office missing from the exhibit -- but for good reason!

"He had three dogs -- Pasha, Vicki and King Timahoe, and he actually kept Milk-Bone biscuits in the Oval Office for them. I don't think they want stale dog biscuits here," he jokingly admitted.

By: Marah Alindogan