SHOCK REPORT! Prince Harry accused of being in 'royal love triangle' with Kate Middleton and Prince William
Kate and Harry, 27, have been photographed whispering and giggling together on a number of occasions, which has prompted one magazine to claim that their 'painfully inappropriate flirting' resulted in a 'blow-up' between Kate and Wills, both 30.
Harry and Kate looked particularly close was on the balcony of Buckingham Palace during the Queen's Diamond Jubilee celebrations in June.
They also shared jokes during the Olympic Torch relay in London last month and at the equestrian event arena in Greenwich last week.
But a person close to the royals says that Harry and Kate - who recently launched their own charity with William - are so friendly because they work together professionally and have the same group of friends.
'What you have to remember is that [Harry] has known Kate for many years - almost as long as his brother,' the friend tells the Daily Mail.
'I know Prince Harry is absurdly proud of the Duchess as his sister-in-law, and is very supportive and protective of her.'