How do you not notice something like this? The Prado museum in Madrid announced that it had a twin of the Mona Lisa (La Joconde / La Gioconda), which had been hanging on display for years without anyone noticing. It is believed to have been painted by one of da Vinci’s disciples. The article says that this copy appears better preserved and Mona Lisa looks younger.
Once again, how do you not notice that you have the Mona Lisa hanging on your walls?
On a personal note, I am rather sad that this news breaks now rather than a couple of years ago. Two Januaries ago I was in Madrid and had an opportunity to spend a few minutes (only a few minutes sadly) at the Prado. I would definitely have tried to see this picture if I knew it was there. And the Prado is a very nice museum by the way. They have some wonderful works by Goya and Velasquez including the latter’s Las Meninas (The Maids of Honour). This alone is worth the trip to the museum. The collection is very large and it is worth the best part of a day. As I recall it, photography was not allowed inside.
The street with the Prado also contains two other major Madrid museums Thyssen-Bornemisza and Reina Sofia. From the latter comes this photograph of Picasso’s Guernica Composition Study. This was the only museum that allowed photography (must be because most of the stuff was ugly modern art). The only major work was not allowed to be photographed.