The 82-year-old head of state, who has been on the throne for half a century, has cancelled her appointments for the week.
In recent days, Queen Margrethe was pictured at several events in London to mark Queen Elizabeth II’s death. She also attended the Queen Elizabeth’s funeral.
At Westminster Hall on Sunday, on the eve of the late Queen’s funeral, she joined the crown prince to pay her respects at the lying-in-state.
At Westminster Abbey the following day, she sat in the same section as monarchs from other European nations, including King Carl XVI Gustaf of Sweden, Prince Albert II of Monaco and King Philippe of Belgium.
She and Queen Elizabeth were third cousins, both being descended from Queen Victoria.
Queen Margrethe, who has been vaccinated against the coronavirus, was also diagnosed with COVID-19 in February this year, showing mild symptoms at the time.