The nation’s royal palace said the prince, who is tenth in the line of succession, visited Spain for an internship on May 26. The 28-year-old then visited a party on May 28. He then tested positive. In total it is believed 27 people attended the party.
Lockdown restrictions in Córdoba, the southern city Joachim visited prohibits gatherings of more than 15, according to the BBC.
Police have launched an investigation into the party.
Those who are found to have breached lockdown face fines up to €10,000 (£9,000).
Everyone said to have attended the party is believed to be in quarantine.
This includes Prince Joachim, the youngest son of Princess Astrid, the brother of King Philippe.
Rafaela Valenzuela, a representative of the Spanish government in Córdoba, has said on the party: “I feel surprised and angry.
“An incident of this type stands out at a moment of national mourning for so many dead.”
At the time of writing, Spain has had over 239,000 confirmed coronavirus cases.
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This has caused further protests after workers discovered the news on Thursday.
Though 3,000 direct jobs have been affected by the closure, unions say the closure will affect as many as 25,000 jobs indirectly.
Nissan reported a $6.2billion (£5.02billion) loss for the fiscal year ending in March.
This is the first time since 2009 the Japanese car manufacturers have reported a loss.
A plant in Indonesia will also be closed.
Joachim is not the only royal to come down with coronavirus.
Charles, Prince of Wales tested positive but has since recovered.
Prince Albert II of Monaco has also tested positive.
Both men are continuing to self-isolate.