Bill Clinton portrait contains hidden reference to Lewinsky's blue dress

A Philadelphia artist has disclosed that his painting of former President Bill Clinton for the US National Portrait Gallery contains a secret reference to Monica Lewinsky's infamous blue dress.

Nelson Shanks told the Philadelphia Daily News a shadow beside Clinton refers to the dress and a symbolic nod to the shadow of the affair on his presidency.

"If you look at the left-hand side of it there's a mantle in the Oval Office, and I put a shadow coming into the painting," Shanks told the newspaper.

He said the shadow beside Clinton, who is pictured standing in front of a hearth, "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," said Shanks, 77.

"It is also a bit of a metaphor in that it represents a shadow on the office he held or on him."

Lewinsky was an intern at the White House at the time of the sex scandal that resulted in her blue dress being stained with Clinton's bodily fluids. Clinton repeatedly denied an affair, but later admitted to a relationship with Lewinsky that was "not appropriate" and "wrong".

The stained dress became a key piece of evidence in Ken Starr's special investigation of the 42nd president.