This is the Portrait of a Lady by Bronzino. Painted in the Italian north, this work showcases the artist's skill at capturing the essence of his subjects. Take a closer look at her costume - it suggests that she is a Florentine noblewoman from the late 1570s and 1580s. It's likely that the portrait dates back to that time period.
Notice how the style of the portrait is similar to those painted by Bronzino himself, who was a court artist to Cosimo I de' Medici, Duke of Florence and later Grand Duke of Tuscany. The opulence of her costume is also reminiscent of portraits done by Alessandro Allori, another artist who worked in the same circle.
Interestingly, this portrait has been attributed to Bianca Cappello, Francesco's mistress and wife, although she doesn't bear a strong resemblance to her. It may be that this is an invention based on several Medici ladies painted by Bronzino.
Portrait of a Lady hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.