Prince Harry may not be able to meet his new niece or nephew until mid-May unless the royal baby puts in a speedy appearance.
Harry is flying back to Australia later today to spend time with Australian Army units in Perth and Sydney before he embarks on an official tour of New Zealand from May 9 to May 16.
The Duke and Duchess of Cambridge's second child is due any day now and Harry jetted in to the UK for a brief stay to present medals at the London Marathon on Sunday after a trip to Turkey for the Gallipoli centenary commemorations.
A Kensington Palace spokesman said, when his short stop off was announced: "He will then privately travel back to Australia on Monday 27th April to begin the second phase of his military attachment to the Australian Defence Force."
Harry will have time to make a last minute dash to the hospital if the baby is born before he leaves to take his flight.
Bookmakers Ladbrokes said William and Kate's fourth wedding anniversary on Wednesday April 29 is now one of the favourite arrival dates at 4/1.
Monday April 27 has odds of 9/2, with Monday being a popular day to be born for the Cambridge family. George was born on a Monday and so was William in 1982.
William and Kate's baby - who will be fourth in line to the throne - is due before the end of the month and Kate plans to give birth at the exclusive Lindo Wing at St Mary's Hospital in Paddington, London.
Kate said the baby was expected to arrive mid to late April, prompting some speculation she might already be overdue. Fewer than one in 20 women give birth on their due date. On the NHS, i nduction is offered to women who go two weeks overdue.
Some believe labour is influenced by the lunar cycle and the arrival of a full moon, and the next full moon is on May 4.
The suggestion is that the moon's gravitational pull affects the amniotic fluid in the same way it affects the water in the sea and rivers.
When Kate gave birth last time on July 22, it was the day of a new full moon.
Ladbrokes has set the odds of the baby being a girl at 8/15 and 11/8 for a boy. Alice remains the favourite girls' name at 5/4, while Charlotte is 5/1. Arthur is the favourite boys' name at 12/1 and James has odds of 20/1.
A punter who has bet £10,000 that the Duchess will give birth to a girl has revealed he only took the gamble because his wife is convinced the baby is a princess.
The anonymous man, in his late 30s and from Manchester, said: "I'm not really bothered by the royals, but I'd just had a big win and my missus reckons it's a girl, so that's a good enough reason for me."
He will collect more than £15,000 in winnings, which includes his original bet, if Kate has a daughter.