Cameras have caught the husband of the president of Finland sneaking a peek at a Danish princess's cleavage during a state dinner.

Pentti Arajarvi was sitting next to Princess Mary of Denmark at an event hosted by her mother-in-law, Queen Margrethe.

Unaware that he was being filmed, Arajarvi, 63, stared down the 43-year-old princess's cleavage as she turned away to watch a speech.

He was caught in the act when she turned suddenly towards him, swinging his head upwards to stare at the ceiling of Copenhagen's Amalienborg Palace with exaggerated nonchalance, while she covered herself with her hand.