Prince Harry shares a giggle with Kate Middleton at the Queen's birthday...

Prince Harry shares a giggle with Kate Middleton at the Queen's birthday...

Perhaps Prince Harry had overheard one of his grandfather's famous gaffes, or he'd spotted an error in the order of service.

But as he leaned over to whisper in the Duchess of Cambridge's ear at St Paul's Cathedral today as the royals attended the Queen's thanksgiving service, his brother certainly wasn't in on the joke.

Harry was seen leaning in to speak to Kate as she titled her head towards him to listen, and whatever the naughty royal had to say left the Duchess in fits of giggles, despite the solemnity of the occasion. Meanwhile Prince Williams stared stoically in the other direction, not sharing in the pair's mirth.
The trio are known to share a close relationship, and with Harry remaining single for the time being he is often the third party in their relationship.

Indeed, he didn't even glance in their direction to find out what was so funny.
The body language revealed a close friendship between Kate and her brother-in-law who were also seen laughing together as they made their way down the aisle of the cathedral to take their seats at the front.
In that instance, they were laughing over a near miss which saw Kate almost get her heel stuck in a grate.

Luckily William alerted his wife before she ran into trouble and she shared a laugh with Harry about the potential mishap.
Today's celebrations saw senior members of the royal family, as well as the extended family, gather to give thanks for the Queen's longevity.
The young royals stole the show as they joined hundreds of politicians, dignitaries, celebrity guests and the extended Royal Family for a special thanksgiving service at St Paul's Cathedral, central London, this morning.

Kate stunned in a powder blue Catherine Walker coat dress with a lace embellished front, which she paired with a cream fascinator decorated with white corsages.
She wore blush suede court shoes - the high heels of which almost caused the mishap with the grate.
The ceremony, led by the Archbishop of Canterbury Justin Welby and attended by a star-studded congregation including Princesses Beatrice and Eugenie.

Former prime ministers John Major and Tony Blair and television personalities Clare Balding and David Attenborough were also there for the service which kicks-off a three-day series of festivities in the capital to mark the Queen's birthday.
Princesses Beatrice and Eugenie, Prince Edward's daughter Louise and son James, Princess Anne and Sophie, Countess of Wessex, and the Prince and Princess Michael of Kent were also in attendance - as were a host of politicians including David Cameron, George Osborne and Jeremy Corbyn.
During the special service, the Archbishop of Canterbury praised the way the Queen had ruled 'through war and hardship, through turmoil and change during the course of her 90 years' and asked the congregation to look back on her rule 'with deep wonder and profound gratitude'.