The Prime Minister was pictured with President Obama and Helle Thorning-Schmidt, the daughter-in-law of Lord Kinnock, the former Labour leader, huddled round the Dane's mobile phone.
Danish Prime Minister Helle Thorning-Schmidt (GETTY IMAGES)
The trio faced criticism on social media for not treating the event with enough reverence.
But Mrs Thorning-Schmidt said the picture showed all three leaders were "just people". Related Articles
"It wasn't inappropriate," she told Danish daily Berlingske. "There were lots of pictures taken that day, and I just thought it was a bit fun. Maybe it also shows that when we meet heads of state and government, we too are just people who have fun."
She added: "There was a sadness, but it was basically a festive event that also celebrated a man who has lived for 95 years and achieved so much in his life. There was dancing on the stands... And then we took a really fun selfie."
"In my defence I would say that Nelson Mandela played an extraordinary role in his life and in his death in bringing people together," he said. "So of course when a member of the Kinnock family asked me for a photograph, I thought it was only polite to say yes."
"I later read on social media that Michelle Obama seemed to be rather peeved on seeing the Danish prime minister take the picture," said Roberto Schmidt. "But photos can lie. In reality, just a few seconds earlier the first lady was herself joking with those around her, Cameron and Schmidt included. Her stern look was captured by chance."