The birth of Prince William in 1982 was a lesson for royal watchers in judicious planning: baby due dates are not set in stone.
Not only can Mother Nature have other ideas, but the arrival of a new heir to the throne is understandably cloaked in secrecy.
Diana, Princess of Wales, is said to have leaked a false date to the media, claiming that William was due on her 21st birthday, July 1, when in fact he arrived 10 days earlier on June 21.
To keep the pressure off the young expectant mother, the royal family maintained the illusion throughout her pregnancy, sending the world's media into overdrive when she went into labour earlier than they anticipated.
Thirty-one years later, speculation is mounting that the Duke and Duchess of Cambridge may have employed a similar ruse.
In May, Buckingham Palace said that the royal baby would be born "mid-July".
A source then claimed the Duchess had announced July 13 as the official date during a family barbecue. Since then, various other suggestions have been made as to the "true" due date, ranging from July 11 to July 17 - but a combination of recent events has raised suspicions that the Duchess could give birth as early as this week.
First, Marcus Setchell, the Queen's former gynaecologist, who postponed his retirement to deliver the baby, told guests at a charity cricket match on Monday that he had stopped drinking in preparation. "He said he's got to be primed and ready for the call from the Palace at any moment," a guest said. "He hasn't touched a drop for two weeks."
Then, on Tuesday, the world's media started assembling outside the Lindo Wing of St Mary's Hospital, Paddington, where the Duchess will give birth. A notice by the main entrance of St Mary's appeared this week, block-booking four parking spaces for the entire month for an unnamed "event". The hospital's taxi rank has been suspended, too - although only until July 15.
Add to that the huge speculation after the Duchess failed to accompany her husband to a recent wedding in Alnwick, Northumberland and it's little wonder that bookmaker Paddy Power has slashed odds on a birth this week from 8-1 to 4-1. Indeed, Twitter was abuzz with rumours that the Duchess had bypassed the press pack and was already in labour.
So, could the wait for Baby Kate end sooner than we think? St James' Palace revealed last month that the Duchess intends to give birth naturally, rather than opting for an elective Caesarean, which makes pinpointing the due date somewhat difficult. Royal watchers have also referenced the popular notion that first-time mothers often give birth late. "The due date is pretty irrelevant," says royal biographer Penny Junor. "Most first babies are a couple of weeks late - but say that to some mothers and they'll say they had theirs early."
Camera crews, photographers and royal reporters from across the world continue to flock to St Mary's - so do they know something we don't? Yesterday, two television crews - Associated Press and American network NBC - were seen camped outside the hospital. Sky, BBC and others are expected to set up on Tuesday.
Those present have marked out their spaces on the pavement using masking tape - spots for around 160 photographers and television crews have been claimed so far. Photographers say some US networks have hired 24/7 security guards to secure their camera positions and others are rumoured to have booked taxis to park permanently in the spaces they want for their satellite trucks.
Bookies, too, are gearing up for an early date. Paddy Power has an unprecedented 18-year accumulator bet on the royal baby, while William Hill has odds of 16-1 on today as the birth date. Around the world, royal watchers are preparing, too.
Last week, the Finnish Government sent a maternity package containing clothing, towels and toys to Kensington Palace. In its attempt to report the news first, the American magazine Life & Style even printed the headline "Kate's Dramatic Delivery" on the front of its July 8 issue, out this week. "Her family and a security team rush to the hos-pital - but William's torn from his wife's side," reads an ill-judged teaser.
Prince William will not be taking any time off from his duties at RAF Valley on Anglesey before the birth (so no clues about the due date there).
When the Duchess does go into labour, it has been suggested that the Duke will have a helicopter on standby to take him to London.
Should the Duke not make it to the Lindo Wing in time, both Carole and Pippa Middleton are reported to be on standby to attend the birth.
As ever bigger crowds amass outside the hospital, Penny Junor says the game may be up.
"The only point in trying to get a bit of privacy is if you can steal a march on everyone by going into labour long before anyone's expecting it. There is no way she is going to be able to sneak into the Lindo Wing unnoticed. But maybe the ruse is that she's not going to have it at St Mary's. I'd be surprised if Kate were playing games, but who knows?"