A 21-gun salute has taken place in Copenhagen as the country celebrates a royal birth. A delighted Crown Prince Frederick has announced that his Australian wife Princess Mary has given birth to a son. No name was immediately available for the baby, who weighed in at 3.5 kilograms and measured 51 centimetres.Frederick’s mother, Queen Margrethe, and the royal family are highly popular in Denmark, and the monarchy is said to be Europe’s oldest. Prince Frederick married Mary Donaldson in May last year after a fairytale romance. She was a real estate agent in Tasmania before the relationship, which began in a Sydney bar during the 2000 Olympics. Now she is in line to become the first Australian to be a queen.