This is the "An Adoring Angel" by Moretto da Brescia, painted around 1540. It's an oil on wood piece that originally would have been part of a larger altarpiece, with shutters to protect and embellish it. Each shutter had a saint on the outside and an angel on the inside - you can see one of those angels here.
The central image these shutters would have flanked is now missing, but we know what it would have depicted because of the inscriptions below each angel's feet. The Latin says "COELORUM", which means 'of the Heavens', and when read together with the other inscription, it forms a message: AVE REGINA COELORUM - 'Hail Queen of the Heavens'. It suggests that the missing central image was a picture of the Virgin Mary crowned in the heavens.
The angel itself is quite striking. The androgynous figure claps its hands in prayer, with its golden hair flowing to one side as if it's moving towards where the central image used to be.
An Adoring Angel 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.