Queen Ingrid never held the title Dowager Queen but was styled Queen Ingrid for life. Meaning that during her daughters reign and while she was still alive Denmark oficially had two queens. Though only one Monarch.
This was the request of the young Monarch back in 1972 when her father had just died, that her mother not be dowager queen, but to be titled Queen Ingrid also in future.
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Margrethe did much more than letting Ingrid keep her title as Queen. She included Ingrid as a regent, when she herself was out of the country. This was done in the summer of 1972, when Queen Ingrid signed the Danish Constitution and thereby swore to uphold it. It was the first time in Denmark that a regent was picked from outside the line of succession. It was a great honour and signalled that even though Ingrid was now a widow , she was still a very important member of the royal family.