Queen Mary surprised guests at her latest engagement as she spoke about "the joys – and sorrows" of parenthood.
The Danish royal attended the Realdania's conference "Our Quality of Life" at the Lokomotivvaerkstedet in Copenhagen on Thursday.
The philanthropic association released a comprehensive study of quality of life on 20 March, coinciding with International Day of Happiness.
The study polled 122,000 people in Denmark and asked them about factors affecting their happiness.
Mary, who looked chic in a Sixties-inspired collared Prada dress, delivered a surprise speech during the event, in which she spoke about the impact of parenthood.
She opened her speech by saying: "'Overall, how satisfied are you with your life right now?'
"This is one of the questions behind the comprehensive study of quality of life that Realdania is publishing today (and which you are reading)."
© Getty ImagesShe continued: "How many people here have children? You know the joys – and sorrows – of parenthood.
"Studies show – to my great surprise – that new parents' happiness in life drops quite significantly and only levels out when the children move away from home. Yet we would never trade our children for anything… almost never.
"Having children is a good example of how meaning in life does not always coincide with the greatest possible joy in life."
Queen Mary shares four teenage children with her husband, King Frederik – Crown Prince Christian, Princess Isabella and twins Prince Vincent and Princess Josephine.
Christian began his gap year last September, with a three-month trip to East Africa, where he worked on two farms and learned about conservation.
Isabella will celebrate her coming-of-age birthday next month with a special youth-centred event and a theatre performance.
© GettyMary is known for her work on issues relating to health, including mental health, and is an advocate for women and children.
In 2007, when she was Crown Princess, she set up The Mary Foundation to improve the lives of children, adults and families, who as a result of their environment, find themselves socially isolated or excluded from society.
© Getty ImagesOn Monday, Mary visited a school through her work with her foundation, focusing on the School Force initiative, which aims to improve the well-being of students.
It marked a return to her public duties after the Danish Queen was forced to cancel engagements last week amid illness.
