Now it can be told! Mona Lisa couldn't help her beguiling smile because she had just given birth to her second son when she sat for the painting, says a French art expert.

The conclusion was made based on Mona Lisa's dress which was covered in a thin, transparent gauze veil. "This type of gauze dress... was typical of the kind worn in early 16th century Italy by women who were pregnant or who had just given birth. This is something that had never been seen up to now because the painting was always judged to be dark and difficult to examine," said Bruno Mottin from French Museums' Centre for Research and Restoration.

Computer scientists from Canada's National Research Council (NRC) used special 3D technology to scan the painting on both sides to get a high resolution 3D image data that uncovered its secret. Based on this image, the centre also said that Leonardo daVinci made the painting to commemorate the birth of the second son of the lady Mona Lisa, around 1503.

She must have really been high on baby love to be able smile like that centuries before epidural was invented!