Britain`s Prince William and his wife Kate visited a charity in London on Friday on what media said would be her last public engagement before she gives birth.
The Duchess of Cambridge, who is around eight months pregnant, is already mother to one-year-old Prince George, the third in line to the throne.
"We asked her when it`s due and she said April. End of April," said Paul Reardon, 50, who chatted to the royal couple when they went on a walkabout in the Gipsy Hill area of south London.
Another onlooker standing nearby, Helen Scholes, 46, told reporters: "William said number one is a life change and number two is a game changer."
Royal officials announced that Kate was pregnant with her second child in September but have remained tight-lipped about the due date for the baby and have not said if it will be a boy or a girl.
On Friday, William and Kate visited a church to hear musical performances by young people who have turned their lives around thanks to the eXceL project charity.
"William said he couldn`t wait for the baby to be born. He said he wanted it now, he couldn`t wait another minute," Reardon said.
Kate is expected to give birth at the private maternity wing of St Mary`s Hospital in London where she also had Prince George.