The idyllic portrayal of a young child and a baby in the country, surrounded by toys and gardening implements, is titled Franzi und Max in Laxenburg.
Less than 20 years later, the elder brother was to become Franz Joseph I, Emperor of Austria and King of Hungary, while his younger sibling was destined to be Maximilian I, Emperor of Mexico.
They are shown playing in the grounds of Laxenburg Castle, a Habsburg residence 12 miles from Vienna and the birthplace of many a member of the royal family.
Franz Joseph (1830-1916) was Emperor of Austria, King of Hungary, Croatia and Bohemia, and monarch of other states of the Austro-Hungarian Empire from 1848 to his death. Two years afterwards, defeat in the First World War destroyed the empire.
Maximilian, an Austrian archduke, was invited to be emperor of Mexico in 1864 after the country had been invaded by the French, to establish a new pro-French monarchy.
Just three years later, the French had withdrawn, the empire collapsed and Maximilian was executed by a firing squad (as famously depicted by Edouard Manet in a series of four paintings including the damaged work now in the National Gallery, London).
The double portrait sold in Munich was the work of Peter Fendi, who had become court painter in the very year it was executed. He was a prolific artist and equally accomplished as a painter, draughtsman and lithographer.
The guide for the 6 x 8in (16 x 21cm) watercolour offered in Munich on February 9, which came from a south German collection, was €5000.
The international buyer who bought it had to pay three times as much: €15,000 (£13,275).