Kate Middleton told families and volunteers at a children's centre for struggling parents that she is expecting her second child to arrive by "mid-to-end" of April.
Kate visited Brookhill Children's Centre in Woolwich, south east London yesterday, where she attended a coffee morning before watching a training session for volunteers and visiting an on-site creche.
Wearing a blue and white Asos maternity dress with black shoes, she chatted with families supported by Home Start charity, which runs the centre, and some of its network of 15,000 volunteers.
Volunteer Christie Osborne (49) was among those the duchess sat and spoke to at the coffee morning.
"I told her she is beautiful and that she's got a tiny little bump. I asked when her baby is due and she said mid-to-end of April," Ms Osborne said.
The duchess was showered with gifts during the visit.
She laughed as Ayo, a three-year-old boy in the centre's creche, presented her with a card made by children as he exclaimed "ta-da!".
The duchess asked the confident little boy: "It's a very big card isn't it? What's on the front?
Ayo replied: "It's a flower!"
Agnieszka Cierpol, who works with Ayo at the centre, said: "He comes in every day for three hours.
"He's a very bright child and from the beginning he could talk.
"Most of the children here have problems, they can't speak or they have issues with their social skills, but he is very smart."
Kate also received a goodie bag for Prince George embroidered with his name and a bouquet of flowers.
Meanwhile, the duchess sent online shoppers into a frenzy after being spotted in the Asos dress.
Kate chose the black polka dot number, teamed with a black clutch bag and matching suede heels for her visit to the centre.
Within 30 minutes of her stepping out of the car in the wrap dress, it had sold out in all sizes on the retailer's website, being snapped up by people keen on recreating her look.
However, Asos says the frock is due be back in stock next week.
Costing £35 (€48), it is described as a maternity "wrap skater dress in spot print" with three quarter length sleeves.