Princess Mary's fairytale marriage to Crown Prince Frederick of Denmark would not have happened if the Prince's mother had her way, according to a new book.

'Everything about the Royals', by Royal Historian Alexander von Schonberg claims Queen Margrethe II invited eligible European princesses to Denmark in an attempt to lure him away from Tasmanian commoner Mary Donaldson, the Herald Sun reports.

Von Schonburg claims, "It was just to show Frederick there were alternatives, there were other options, that there are these good looking, fun-loving princesses around."

Speculation suggests that the two visiting princesses were the author’s nieces, German born Elisabeth and Maria Theresia von Thurn und Taxis.

However Prince Frederick's interest in Mary, whom he met in Sydney at the 2000 Olympics, was not to be swayed, with the book apparently claiming he didn’t look at the princesses invited to the palace.

The Queen may have been concerned about how an outsider would handle the pressures of royalty, von Schonburg believes. "I'm sure the Queen of Denmark would have preferred him to marry someone with a similar sort of background," he told the Herald Sun.

He's also quoted as saying, "When she saw he really was determined to marry Mary, of course she supported him."

Von Schonburg said the Queen was concerned about how Mary would cope with the public attention.

"Every move you make, every sentence you utter, everything is commented on.

"If you've grown up in a relatively normal family with liberties and individuality, it can be very hard to take."

Frederick and Mary were married in 2004 and have since extended their family to include children Christian, 3 and Isabella, 20 months.