The Duchess of Cambridge sent online shoppers into a frenzy after being spotted in an Asos dress.

Kate chose the black polka dot number, teamed with a black clutch bag and matching suede heels, for her visit to Brookhill Children's Centre in south-east London.

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, it is described as a maternity "wrap skater dress in spot print" with three quarter length sleeves.

Meanwhile, The Duchess of Cambridge told families and volunteers at a children's centre for struggling parents today that she is expecting her second child to arrive by "mid-to-end" of April.

Kate, who is due to give birth next month, visited Brookhill Children's Centre in Woolwich, south east London, where she attended a coffee morning before watching a training session for volunteers and visiting an on-site creche.

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.

Ms Osborne said: "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."

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.

Marvellous Nyanhi and her son Tinashe handed over the presents, which included an Elmer the Elephant book, a potty training booklet and a colour-sorting clock.

Marvellous, 35, from Plumstead in south east London, said: "The Duchess had a chat with my little one and she asked about the colour of the flowers.

"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."

Home Start, which was set up in 1973, recruits and trains volunteers to support parents with at least one child under the age of five.

The charity helps more than 29,000 families each year who are dealing with issues including isolation, mental health problems, bereavement, multiple births, illness or disability.

It runs four of Greenwich council's 24 children's centres which offer services including early-years education, childcare, family health services and employment and training advice for parents.

Home Start chief executive Rob Parkinson said: "People will have felt that their contribution to family support is really valued because of her visit and that's the most important thing for me.

"The Duchess had a nice chat with of a couple of mums and they were able to share their experiences, forthcoming or otherwise."