Kate, 36, rushed to talk to her daughter and the two-year-old girl was on the verge of tears.
Video footage of his visit to Europe in Germany and Poland emerged from Prince George excited to see the helicopters as a pre-birthday gift, while watching his little sister compose while Kate and William distracted her.
Kate was forced to duck and comfort the young man before embracing her in his arms, while a Prince George was seen sitting inside the helicopter and wandering around the plane in amazement.
Princess Charlotte cheered up later and looked a little happier when she also had to stand inside the helicopter.
The little princess has earned an army of real admirers with her adorable smile and her confident and ardent character.
His mother, Kate, told him previously how he expected his "daughter" daughter, Charlotte, three years old, to keep her older brother, Prince George, under control.
Duchess Kate is known for recycling her favorite looks and today was no different when she arrived at the first World Ministerial Summit on Mental Health in County Hall, aimed at helping improve mental health around the world.
She complemented the elegant look with a taupe crocodile print bag of £ 695 from Aspinal of London, and a pair of dazzling diamond earrings by Mappin & Webb, which cost £ 3,750 and a £ 1,000 pendant by the same designer.
The royal couple, who were acclaimed by crowds gathered on the street outside of County Hall, have been involved in mental health initiatives through their Heads Together campaign.
Kate returned from maternity leave on October 2 after six months of rest to visit the elementary school children at the Paddington Recreation.
They should meet young people in the UK who have had or are dealing with mental health problems and will hear about case studies of mental health projects in the United States and India.