This is the Apotheosis of the Spanish Monarchy by Corrado Giaquinto. It's an oil on canvas painting that dates back to about 1751, and it's a bit tricky to date exactly because of its sketchy nature.
At first glance, you might think this is just a typical allegory of the gods, but take a closer look and you'll see the connection to the Spanish monarchy. Jupiter, the chief deity, is holding a crown alongside his wife Juno, and there's an eagle clutching a thunderbolt – all symbols of power.
Below them on the left are Venus and Cupid, while Bacchus reclines in the corner, crowned with vine leaves. On the right side, Minerva presents a woman to Jupiter, who may be a personification of Spain. And then there's Hercules in the centre, battling the Hydra – an important labour he undertook for the Spanish monarchy.
The painting is quite loose and sketchy, which was typical of Giaquinto's technique. He would have followed this up with more detailed studies before finalizing the work. This particular piece was likely created as a design for a ceiling painting in Palazzo Santa Croce in Palermo, but it's now housed in the Palazzo Rondinini-Sanseverino in Rome.
Apotheosis of the Spanish (?) Monarchy (?) 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.