A new clue to the mystery of Kate Middleton's due date has been revealed.

Kate Middleton Celebrates St. Patty's Day At Final Event Before Giving Birth

On Wednesday, E! News revealed that Middleton told someone when she is due- well, around when she is due to give birth to her second royal baby.

The Duchess of Cambridge apparently broke the new unintentionally to volunteers at Brookhill Children's Centre in Woolwich where she reportedly went to attend a training session and to visit the on-site nursery.

Prince William & Kate Middleton Seek Housekeeper That's Good With Dogs

"I told her she is beautiful and that she's got a tiny little bump," volunteer Christie Osborne, 49, told reporters following Middleton's visit. "I asked when her baby is due and she said mid-to-end of April."

It's not an exact due date, but it's good enough considering fans had no idea when she was due and still don't know the expected sex of the future prince or princess.

Middleton donned a polka dot ASOS maternity dress with black shoes as she enjoyed a coffee breakfast prior to the training session.

The 33-year-old also spoke with other parent and kids who supported the charity, Home Start, that runs the center and it's network of 15,000 volunteers, the publication reported.

During her visit, the princess also received a gift bag for two-year-old Prince George that was embroidered with his name as well as a bouquet of flowers.

The gifts in the bag were a children's book, a potty training booklet and a color-sorting clock. "The Duchess had a chat with my little one and she asked about the color of the flowers," Marvellous Nyanhi said. "She asked me why I'm here so I told her I was a supported family at first because I was in a really bad place at the time, but now I have trained to be a Home Start volunteer."