Pope Benedict XVI has released the final installment in his trilogy on Jesus.

The book, Jesus of Nazareth: The Infancy Narratives, goes on sale in 50 countries today.

In it, the Pope affirms the Virgin birth but says the animals supposedly watching on as Christ was born were "an invention".

That's not likely to stop churches and shopping centres around the world from setting up their annual nativity scenes complete with the traditional baby Jesus in a crib and accompanying set of animal figures.

The Pope believes as much: "No nativity scene will give up its ox and donkey."

Regarding the Virgin birth, he is unequivocal.

"The accounts of Matthew and Luke are not myths taken a stage further.

"They are firmly rooted, in terms of their basic conception, in the biblical tradition of God the Creator and Redeemer."

He also says that the Angels did not sing the good news of Jesus's birth to the shepherds, but rather "said" it to them.

"But Christianity has always understood that the speech of angels is actually song, in which all the glory of the great joy that they proclaim becomes tangibly present," he explained.

The first two installments, which looked at his public ministry and death, quickly became bestsellers and the third book is expected to be just as popular over the Christmas season.