Crown Princess Mary and Crown Prince Frederik of Denmark are parents again -- to twins, a boy and a girl, born January 8. That brings the tally of their children to four.

Mary Donaldson of Tasmania, Australia, married Prince Frederik in 2004; the following year Prince Christian was born and in 2006 Princess Isabella. At the time of her marriage Princess Mary said that she would like to have several children -- something she has reaffirmed more recently, saying:

"I'd like to have that experience again. That boundless freedom
of childhood is so wonderful. The world is so different for a child,
waking in the mornings, wide-eyed and ready to take it all in."

The birth of twins makes the couple's fertility more than double that of the Danish average of 1.74 children per woman.

Congratulations, Mary and Frederik!