It was discovered in 1998 by astronomers at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.
Petit-Prince was the first asteroid moon to be discovered with a ground-based telescope.
Previously, the only known moon of an asteroid was Dactyl, discovered by the Galileo space probe, around 243 Ida.
It takes five days to complete an orbit around Eugenia.
The discoverers chose the name in honour of Empress Eugénie's son, the Prince Imperial.