David Beckham has offered words of advice to the Duke and Duchess of Cambridge who are expecting their second child - get more sleep before the baby arrives.

As the father of four children the former England football star is speaking from experience and reacted to news of the royal pregnancy by praising the parenting skills of William and Kate.

His words of support came as Kensington Palace said the Duchess, who is suffering from acute morning sickness, would not attend the opening ceremony of Prince Harry's Invictus Games this evening and other associated events tomorrow.

Speaking during an interview with ITV's Lorraine show, Beckham gave the couple some words of wisdom: "Get some sleep because jumping from one child to two is a big step even though I thought jumping from two to three was bigger."

The former England midfielder was interviewed at New York fashion week where he is promoting his new collection for the brand Belstaff.

Beckham has known William for a number of years having joined forces with him to promote England's bid to host the 2018 World Cup, launched wildlife conservation campaigns with the Duke and been a guest at his wedding.

The celebrity added: "But I'm so happy for them both because they're such great parents and obviously to be great parents and to have the roles that they have, as important as they have, is really incredible and I'm just happy that they're going to have another little one running around the house."

The Duchess will miss tonight's opening ceremony of the Invictus Games which will herald the start of the Paralympics-style sporting spectacle for injured servicemen and women from across the globe.

Kate was also due to attend a solemn Drumhead service at Lee Valley Athletics Centre with the Duke and Prince Harry tomorrow, to remember all those who have died or been injured in conflict, and later, with William, watch Invictus competitors taking part in matches and heats.

But the Duchess is understood to still be experiencing the symptoms of the illness and is being treated at her Kensington Palace home by doctors.

Kensington Palace said in a short statement: "The Duchess of Cambridge will not attend the opening ceremony of the Invictus Games this evening or the athletics event tomorrow.

"The Duchess's attendance on the forthcoming visit to Malta will be kept under review and a decision taken closer to the time."

The Duchess is suffering from another bout of the illness hyperemesis gravidarum which she experienced during the early stages of her first pregnancy.

Kate's pregnancy has not passed the 12-week stage and there is speculation that the royal couple's second child could be due in April next year.

Hyperemesis gravidarum, which affects 3.5 per 1,000 pregnancies, causes severe vomiting and can lead to dehydration, weight loss and a build-up of toxins in the blood or urine, called ketosis.

It is thought her illness began sometime last week and when William visited Oxford University on Monday without his wife to open the institution's new China Centre, he said the Duchess had experienced a ''tricky few days''.

Kate is due to make her first official solo overseas tour from September 20-21, touring Malta to mark the 50th anniversary of its independence.

The Prince of Wales greeted the news that he is to become a grandfather for a second time with joy and said he hoped the baby was a girl.

Charles already has a grandson - Prince George - but yesterday said he would like a granddaughter when he visited the studio of a young entrepreneur who has been helped by his Prince's Trust.

As he left the premises in Bermondsey, South London he met Corey Johnson who congratulated him on becoming a grandfather.

The heir to the throne replied: "I am already. But it's wonderful to be a grandfather again. I'm looking forward to it - but I hope it will be a girl this time."