Judi James exclusively told Express.co.uk that the 2017 video gives an insight into “Kate’s role in the dynamic”.
She claimed: “Kate is calm, dominant and maternal. Her role is to lead and facilitate and all three look comfortable with her in this maternal role.
“She gently emphasises the emotional bond between what she calls ‘you boys’, triggering their childlike state to enable them to be open with each other.”
During the video, William and Harry discussed their grief after losing their mother Princess Diana at a young age, but Kate acted in a supporting and “maternal” role.
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Judi continued: “Kate also nudges and leads the theme with phrases like ‘It’s incredible how you have been able to cope’ and ‘You’re amazingly close’.
“She sounds as though she is facilitating the realisation of the power and the vital importance of that closeness, which might have been a sign that problems were looming.”
Prince Harry mirrors Kate’s body language, according to Judi, by agreeing that having close people around is “important”.
Judi added: “Harry refers to the importance of ‘family and friends that care about you’. Kate looks and sounds empathetic and also wise about the sibling relationship.
“It is clearly possible to see we shouldn’t underestimate the personal loss she must have felt with the breakdown.”
Judi also claimed that the Prince of Wales may have attempted to help Harry with his mental health as a result of this video.
She explained: “Far from a cold and uncaring response to Harry’s grief, this film shows it was William who was actually trying to encourage his brother to open up about his grief rather than rejecting him or trying to get him to ‘bottle it up’.
“Harry tells how ‘both of us have always been open with each other, saying we’ve never really talked about it’ (Diana’s death).
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“The assumption has been that this was down to William, but it seems it was Harry who struggled to discuss it and William who was encouraging him to speak.”
Judi noted how Harry even admitted in the video that it was his brother who encouraged him to talk about his mental health.
She explained: “Harry’s own words are that ‘William always said you’ve got to sit down but for me, it was like I don’t want to think about it’.”
The body language expert argued that the Duke showed “deep affection” for his brother in the video.
“Harry uses postural and verbal echoing of his brother here too, to show deep affection for him,” Judi opined.
However, Prince William, on the other hand, showed similar character traits to his father King Charles.
Judi claimed: “William does show he can be his father’s son though and one throwaway line sounds eerily similar to Charles’s emotionally deflecting line at his engagement interview with Diana.
“For Charles, it was ‘whatever being in love means’ when told he was in love with his bride-to-be. William’s quick ‘Most of the time’ line sounds like a similar deflection when Kate tells the brothers they are ‘amazingly close’.”