Prince William and Prince Harry "were nervous" as they watched their dad remarry, a body language expert said yesterday.

Judi James analysed three photographs taken at the ceremony at St George's Chapel, Windsor Castle, 19 years ago to the day on Tuesday. As the anniversary approaches, the body language expert said Harry and William "had to dig as deep" at the occasion and "suppressed what must have been many negative emotions".

They watched their father, then Prince of Wales, marry Camilla Parker-Bowles nearly eight years after the tragic death of Princess Diana, the mother of his sons. He was married to Diana, who died aged 36, for 15 years before their divorce in 1996.

Recalling Charles and Camilla's wedding, Ms James said: "Few stepchildren will have had to dig as deep as Diana’s two devoted and loyal sons did when attending the marriage of their father to Diana’s sworn rival Camilla. It is to the brother’s credit that they suppressed what must have been many negative emotions for the sake of their father and the need for family unity.

"The pair opted for two key motivational techniques: overkill displays and muscle memory formalities. The first provides an outlet for any building tension and rising adrenaline and the second allows you to go into automatic pilot mode."

Prince Charles and Camilla wed on April 9, 2005 - 19 years ago on Tuesday (
Image:
PA)
Prince Harry and Prince William are pictured leaving the chapel on the wedding day (
Image:
Getty Images)

The expert told The Sun the ceremony was harder for William and Harry, then aged 22 and 20 respectively, than the public may have first thought. She said body language suggests the siblings were expressing "shared grief" at the ceremony and, when Charles and Camilla took the vows, Harry's "troubled expression seems to express it all."

"His loyalty to his mother conflicted with a desire to play ‘happy’ for the sake of his father," Ms James continued, as she assessed images taken at the ceremony on April 9, 2005. It was some 34 years since Charles and Camilla's relationship started, it is understood, after the pair regularly met at polo matches.

But Charles tied the knot with Diana in July 1981, then aged 32 and 20 respectively, at a large ceremony in St Paul's Cathedral. The People’s Princess, though, called the relationship “tricky” as she knew how much Charles loved Camilla.

She claimed that before her wedding, she found out Charles had a bracelet made with the initials "G" and "F" for Gladys and Fred – pet names Camilla and Charles had for each other.

She also found photos of Camilla in Charles' diary on their honeymoon, as well as cufflinks with the initials "C" and "C" intertwined. Five years on from their spectacular wedding, Charles and Diana's marriage was lost – with Camilla firmly back in the picture.