By DAILY MAIL REPORTER
Long may he rein: Most of the tourists and onlookers will not have recognised the Duke
Dressed in a red guardsman's uniform, riding confidently with one white-gloved hand on the reins and the other at his side, this could be any other soldier rehearsing for Trooping the Colour.
But take a closer look, for there is something distinctly familiar about this particular soldier.
One day he will reign as King, but today the Duke of Cambridge was holding the reins of a distinctive mottled grey horse called Wellesley.
Familiar face: The bottom half of Prince William's face is just about visible under his hat
Prince William rode down The Mall from Buckingham Palace on a horse today as he took part in a rehearsal for Trooping the Colour - a ceremony held in honour of his own grandmother's to celebrate her birthday.
Most of the tourists and onlookers will not have recognised the Duke, whose eyes were shaded by his traditional tall hat.
William rode behind the Duke of Kent, Colonel Scots Guards.
Trooping the Colour: The Duke of Cambridge is taking part in the ceremony to honour his grandmother, The Queen
First time: William, who served in the Blues and Royals, has not ridden at Trooping the Colour before
Spot the royal: After about an hour at Horse Guards Parade, the procession made its way back down The Mall
The event, known as the Colonel's Review, takes place a week before Trooping the Colour, which marks the Queen's official birthday.
Hundreds of soldiers were out on display for the ceremonial occasion, parading along The Mall to Horse Guards Parade in bright sunshine.
William, who served in the Blues and Royals, has not ridden at Trooping the Colour before.
After about an hour at Horse Guards Parade, the procession made its way back down The Mall.
The cavalry appeared as a sea of red shimmering the heat, with William at the centre.
Pomp and ceremony: The soldiers make their way to the Horse Guards Parade to take part in the Colonel's Review
Ceremonial: Soldiers from the Irish Guard make their way to the Horse Guards Palace with their mascot, an Irish wolfhound
He was wearing the same red tunic of the Irish Guards, with a blue sash, that he chose for his wedding ceremony.
But he donned a bearskin rather than forage cap.
William was was made Colonel of the Irish Guards in February.
He rode the horse around into the palace forecourt, holding the animal steady for five minutes as the ceremonial parade came to an end.
Attention: Soldiers from the Grenadier Guards take part in the Colonel's Review
Line up: The cavalry appeared as a sea of red shimmering in the heat
And as he and the Duke of Kent turned to ride into the Palace grounds the band struck up the national anthem.
William will also take part in Trooping the Colour next Saturday.
A Palace spokeswoman said: 'We can confirm that The Duke of Cambridge will take part in The Queen's Birthday parade.
'He will ride as Colonel of the Irish Guards.
'All Royal Colonels of the Foot Guards including The Prince of Wales (who will ride as Colonel of the Welsh Guards) ride together as determined by the Major General of the Household Division.'