Prince William got so excited cheering on his favourite soccer team that he may have let slip the sex of the baby he and Kate Middleton are expecting this month.

Leaping to his feet in the stands, the prince celebrated with friends on April 10 when Aston Villa’s Jack Grealish kicked the winning goal in the team’s championship match against Cardiff City.

Pumped, William told fans, “I’m going to insist the baby is called Jack,” reported The Mirror.

After a – pregnant – pause, he added, “Or Jackie”.

Still, despite the possible gaffe, another report in UK newspaper Express claims Kate, 36, and William, 35, still do not know if their third child will be a prince or princess.

The couple opted not to be told during routine scans, it reported.

Whatever the truth, the official news of the birth, complete with details of the baby’s gender, weight and time of arrival, will be announced on a notice placed outside Buckingham Palace on an easel by a royal footman.

The baby is due mid to late April, according to The Telegraph. Kensington Palace has not named a specific date but William said it could make its entrance “any minute”.

William raises a Guinness with Kate at the annual Irish Guards’ St Patrick’s Day parade on March 17. Photo: Getty

Royal baby watch is already happening at St Mary’s Paddington, where Kate is expected to give birth in the hospital’s exclusive Lindo Wing.

The outside of the wing has been painted and parking restrictions were put in place at St Mary’s on April 9.

Signs say the restrictions will remain until April 30, which royals experts have said suggests the baby is probably due midway between the two dates, around April 16.

The reason given for the no-go zones? An ‘event’.

Crowd barriers are in place on the street outside for television crews, journalists and photographers.

While media gathered weeks ahead for the 2013 birth of Prince George, this time Kensington Palace has said they will only be allowed access once the Duchess of Cambridge is in labour and with William at the hospital.

Kate will be looked after by a team headed by Alan Farthing, the Queen’s surgeon-gynaecologist, and Guy Thorpe-Beeston, surgeon-gynaecologist to the royal household. Both were at the births of George, 4, and Princess Charlotte, 2.

With George, Kate left the Lindo Wing the day after giving birth but with Charlotte stayed only hours before heading home to Kensington Palace.

Kate started maternity leave on March 23, after carrying out 38 official engagements this year.

She had William at her side for her final day’s work. With Kate in heels, they watched a wheelchair basketball game then had lunch at a community centre.

The Cambridges were childless at a Windsor Easter service on April 1. Photo: Getty

While her public duties are done for now, Kate’s private role as a mother-of-two saw her armed with reusable bags and browsing the aisles at a Waitrose supermarket on Easter Monday.

Dressed in a peach Joseph coat and black boots, the duchess reportedly grabbed a free hot coffee and a cut-price bunch of coriander before loading her shopping into the back of her Range Rover herself.

A fellow shopper told The Daily Mail she said hello to Kate, who replied, “Hi, hello.”

Kate then drove to Anmer Hall, the Cambridges’s sprawling country home on the Queen’s Sandringham estate.

Whatever date the baby arrives, Kate will be back in the public eye on May 19 for the Windsor wedding of Prince Harry and Meghan Markle, then at Buckingham Palace for June’s Trooping the Color.