FORMER Hong Kong resident Princess Alexandra of Denmark, 34, gave birth to a boy yesterday. It was her first child, the Danish television station DR-1 reported last night. The baby weighed 2.7kg and measured 48cm. The prince is Queen Margrethe's first grandchild and is third in line to the throne after his uncle, Crown Prince Frederik, 31, who is unmarried, and father Prince Joachim, 30. 'Suddenly there was a son,' a jubilant Prince Joachim told reporters at Copenhagen's University Hospital. He attended the delivery and cut the umbilical cord. Prince Joachim married the then Alexandra Manley - a former Island School pupil and daughter of a British father and Austrian mother, with a paternal Chinese grandmother - on November 18, 1995. The romance started at Christmas, 1994, in Hong Kong where the prince worked at the Danish shipping firm Maersk while his bride, an economist, lived in Discovery Bay. The new-born prince is the first seventh-generation member of the House of Gluecksborg.