A palace official said the child, Felipe Juan Froilan, was handling a small-calibre shotgun on Monday at a country estate owned by his father when the gun went off and hit him in the right foot. His father was with him at the time.
Under Spanish law, it is illegal for children under 14 to possess or discharge firearms. A palace official declined to comment on the infraction.
It is now up to a judge to decide whether to punish the boy’s father. Spain’s Civil Guard police said he could face a fine of up to €6,000 (almost £5,000).
Widely known in Spanish media as simply Froilan, the boy is the son of Princess Elena, the eldest of King Juan Carlos and Queen Sofia’s three children. His father is an aristocrat and banker named Jaime de Marichalar. The couple were divorced in 2009.
The royal palace said the boy underwent surgery on a toe overnight and will be in hospital for a few days. Froilan is the eldest of eight royal grandchildren.
It was not the first shooting incident in the Spanish Royal Family’s history. In 1956, Juan Carlos was handling a gun that accidentally went off and killed his 14-year-old brother.
The accident happened in Estoril, Portugal.