EU leaders are scheduled to meet face-to-face on July 17 for the first time since the outbreak of the coronavirus pandemic to discuss the European budget and the plans for recovery from the Covid-19 crisis.
"I'm so looking forward to marrying this man," wrote Frederiksen in a post that featured herself and her fiance Bo Tengberg. "The Council meeting in Brussels has been convened exactly on the Saturday in July when we had planned our wedding. Damn. But, I have to do my job and protect Denmark's interests.
"I'm looking forward to saying yes to Bo (who is fortunately very patient)," she added.
Denmark has recorded 12,836 coronavirus cases and 603 deaths, according to figures from Johns Hopkins University.
It was one of the first Western countries to begin easing lockdown restrictions in April after the number of cases in the country remained low.
The leader of Denmark's center-left Socialist Democratic party became the country's youngest prime minister last year at the age of 41.
Last August, US President Donald Trump accused Frederiksen of making "nasty" and "inappropriate" comments, after she called his reported wish to buy Greenland "absurd."