Princess Charlene and Prince Albert
 Princess Charlene married Prince Albert II of Monaco in a civil ceremony on 1st July 2011.REUTERS/Eric Gaillard

Monaco's Prince Albert II and wife Princess Charlene are expecting their first child together.

The royal couple, who married in an opulent ceremony in July 2011, expressed their "immense joy" after finding out that they are set to become parents.

"Prince Albert and Princess Charlene have the immense joy to announce they are expecting a happy event. The birth is due at the end of the year," a statement from the palace said.

Albert, who is the son of the late Prince Rainier III and actress Grace Kelly, met his wife in 2000 when he presided over a swimming race.

They went public with their romance at the 2006 Winter Olympic games before tying the knot five years later.

The baby news comes after months of speculation as to why the South African-born princess, a former Olympic swimmer, had not produced an heir for her husband after three years of marriage.

Their unborn child will replace Princess Caroline - Prince Albert's older sister - as heir to the throne once it arrives.

Albert is already father to 22-year-old daughter Jazmin and 10-year-old son Alexandre from previous relationships.