In a rare glimpse of the strain behind their seemingly perfect marriage, Crown Prince Frederik and Crown Princess Mary have had a disturbing fight, despite the eyes of the world being on them.Glaring at each other, hunching their shoulders and pursing their lips, it was a portrait of the strained couple the palace never wanted you to see.

During a month of celebrations commemorating the 40th anniversary of Queen Margrethe’s coronation, the couple had clearly had enough of the festivities – and each other. First Mary, who is rarely seen without a placid smile, leans into a grumpy looking Frederik as he mutters something to her. Upset and seething, she purses her lips and looks away.

Finally Fred assumes a haughty expression as he glares past his wife, clearly bored and irritated. It’s the kind of exchange shared by many couples, but it’s one we rarely see from this pair, who normally present a united front. What makes the tense scene even more surprising is that it has come at a time when the spotlight is fixed firmly on Denmark’s royals.

With the cream of European society gathered in Copenhagen to mark Margrethe’s ruby anniversary on the throne, there could hardly have been a more public way for the couple to have displayed their marital tension. There’s little doubt that pictures, taken during an exhibition of the Queen’s couture at Amelienborg Palace earlier this month, are a sign that the pressure of raising four young children is getting to the couple.

Read more about Princess Mary and Prince Frederik's argument and see the pictures of the pair arguing in this week's Woman's Day on sale January 23, 2012.