Finally an answer to the world's last unanswered question!

Ok, I actually think this answers two questions... why was she smiling and how, exactly, was her hair styled.

PARIS - Researchers studying 3-D images of the "Mona Lisa" say she was probably either pregnant or had just given birth when she sat for Leonardo da Vinci's 16th-century masterpiece. The clue was something she wore.

Scans turned up evidence of a fine, gauzy veil around Mona Lisa's shoulders — a garment women of the Italian Renaissance wore when they were expecting, a leading French museum researcher, Michel Menu, told The Associated Press in an interview Wednesday. The scans also make clear that Mona Lisa does not have her hair down, as it appears. Most of her tresses are pinned back into a chignon and covered with a veil, Menu said.

The veil "would confirm art historians' hypothesis that Giocondo asked for a painting of his wife to celebrate the birth of his second son," said Menu, chief of the research department at the French Museums' Center for Research and Restoration, which has its offices in the Louvre.

John Taylor of Canada's National Research Council said there were no signs of brush strokes. "That includes the very fine details of the embroidery on the dress, the hair," he said. "This is the 'je ne sais quoi' of Leonardo. The genius. We don't know how he applied it."

"What is amazing and paradoxical about that painting is that people think it's been analyzed but it's exactly the opposite," Rioux added. "This is the most inaccessible painting in the world. Why? Because it's 99.9 percent of the time in the Louvre for the public to view. The last time it was up for examination was 1952."

Mona Lisa's smile has for centuries inspired speculation. In the 1950s, Nat King Cole asked in a song lyric if she was smiling to "tempt a lover" or "to hide a broken heart?"

New discoveries "don't take away the mystery," Menu said. "On the contrary, they merely add another layer to the meaning, which only makes things more interesting."