The artist who painted the Bill Clinton portrait that hangs in The Smithsonian's National Portrait Gallery added an easter egg that contains a veiled reference to the president's infamous affair with Monica Lewinsky.

If you look closely at the portrait, you'll notice a dark shadow that appears on the mantel in the Oval Office just behind Bill Clinton's right shoulder.

Can you see it?

A portrait of former President William Jefferson Clinton by artist Nelson Shanks is seen at the Smithsonian Institution's National Portrait Gallery on Monday, April 24, 2006. Image: National Portrait Gallery, Nelson Shanks/Associated Press

Look closer...there:

A closer look at a portrait of U.S. President Bill Clinton shows a shadow meant to represent the blue dress made infamous by his affair with Monica Lewinsky. Image: National Portrait Gallery, Nelson Shanks/umkc/Mashable/

That shadow, Philadelphia portrait artist Nelson Shanks says, is cast from a blue dress — similar to the blue Gap dress worn by Lewinsky while she had oral sex with President Clinton and contained a semen stain.

Clinton, the FBI later concluded, was its source.

"I could never get this Monica thing completely out of my mind and it is subtly incorporated in the painting," Shanks says, describing the shadow.

"It actually literally represents a shadow from a blue dress that I had on a mannequin, that I had there while I was painting it, but not when he was there," the artist. "It is also a bit of a metaphor in that it represents a shadow on the office he held, or on him."

The Clintons, according to the artist, want it removed from the gallery — though a spokeswoman there denied that rumor to the Philadelphia Daily News.

Lewinsky, for her part, spoke about the dress to ABC's Barbara Walters in March, 1999, telling her that she thought the whole thing was "funny" until she grew "terrified" about being hit with obstruction of justice charges if she washed it.