The Duke of Cambridge, 39, rode a black Household Division charger, named George, as he went through the practice inspection – known as the Colonel’s Review – in central London.
One unnamed source told MailOnline: ‘William’s horse looks drugged. Its head is on the floor. It’s a disgrace.’
A Clarence House spokesman declined to comment.
For the event, William wore his red and blue military uniform adorned with medals, which he teamed with the traditional bearskin hat as he sat on the charger, also festooned in ceremonial regalia.
Horses of the Household Cavalry which feature in such parades undergo special training so that they are desensitised to noise and traffic. They also need to be comfortable standing still for long periods and become accustomed to the weight of extra kit.
The Queen’s birthday on June 2 sees her Household Division troops march and ride on Horse Guards Parade with Her Majesty usually attending and taking the salute.
But this year, the Prince of Wales, the Duke of Cambridge and the Princess Royal will ride on the parade as colonels of the Welsh Guards, the Irish Guards and the Blues and Royals.
Only William was seen at the run-through today, which went without a hitch – unlike last week.
Prince William rose early to take part in the rehearsal of the Queen’s birthday parade in London on Saturday. A military veteran tonight claimed that the prince’s horse appeared ‘drugged’ during the event. The unnamed source told MailOnline: ‘William’s horse looks drugged. Its head is on the floor. It’s a disgrace’
The Duke of Cambridge, 39, rode a black Household Division charger, named George, as he went through the practice inspection known as the Colonel’s Review in central London
William wore his red and blue military uniform adorned with medals, which he teamed with the traditional bearskin hat as he sat on the charger, also festooned in ceremonial regalia. Horses of the Household Cavalry which feature in such parades undergo special training so that they are desensitised to noise and traffic
The famous salute at the real Trooping the Colour is usually performed by the Queen but William has stepped in this year
Prince William salutes as he rides across the parade ground during the Colonel’s Review at Horse Guards Parade
Prince William looked very serious at the rehearsal of the prestigious military birthday event in London for the Queen. Irish Guards wear a blue plume to the right of their bearskin
Soldiers are seen on parade during the Colonel’s Review – the second rehearsal for the Trooping the Colour, which dates back to 1748
The Colonel’s Review is identical to Trooping the Colour, the Queen’s annual birthday parade, which she will not be at
This year, the Prince of Wales, the Duke of Cambridge and the Princess Royal will ride on the parade as colonels of the Welsh Guards, the Irish Guards and the Blues and Royals
Members of the Household Division parade during the Colonel’s Review ahead of the Trooping of the Colour next week
The Mounted Band of the Household Cavalry and the Queen’s drum horses parade during the review today
Two people had to be rushed to a major trauma hospital and three others needed treatment from paramedics after a stand collapsed at the Trooping the Colour rehearsal on May 21.
The ‘terrifying’ incident took place in front of a crowd of ‘shocked’ onlookers who had gathered to watch the event in Horse Guard Parade, London, at around 11am.
Witnesses reported part of the stand collapsed, causing at least one person to fall through into the area below.
Part of the stand was evacuated following the incident, and two people have been taken to hospital by London Ambulance and St John Ambulance for treatment.
Three other people who were hurt in the incident were treated at the scene and discharged without needing hospital treatment.
Last week it was revealed the Queen would not take the royal salute at the Trooping the Colour for the first time in 70 years.
The Irish Guards regiment was formed in 1900 by order of Queen Victoria in response to the numerous acts of bravery and gallantry shown by Irish soldiers during the Second Boer War
The Irish Guards’ regimental mascot – an Irish wolfhound – is taken through its paces during the parade review
Above, the regimental mascot Turlough Mor – also known as Seamus. The canine is one of the biggest dog breeds in the world
The Irish Guards display their regimental flag. Prince William has been Colonel of the 1st Battalion Irish Guards since 2011
During the event, only one colour can be carried (‘trooped’) at a time. The five Household Regiments – Grenadier, Coldstream, Scots, Irish and Welsh Guards each take their turn each year
Prince William, who is Colonel of the Irish Guards, leads the Colonel’s Review on Horse Guards Parade on May 28. The procession can be viewed along The Mall or along the edge of St James’s Park in London
Spectators watch the rehearsal. The ‘colour’ in Trooping the Colour refers to the regimental flags of the British Army which were historically described as such because they displayed the uniform colours and insignia worn by the soldiers of different units
Irish Guards march across the parade ground on Saturday during the 90-minute rehearsal
By sheer coincidence, William’s brother Harry was on horseback yesterday playing a polo match for his team in America
The Queen will not take the royal salute at the Trooping the Colour for the first time in 70 years as she continues to delegate responsibility to senior members of The Firm. She is pictured on the balcony of Buckingham Place during the ceremony in 2019
The news comes as the 96-year-old monarch continues to entrust members of the Royal Family with increased responsibilities as she faces ‘episodic mobility problems’
It came two years after the ceremony had to be scaled back due to coronavirus and took place in Windsor.
This year, the Prince of Wales, the Duke of Cambridge and the Princess Royal will ride on the parade as colonels of the Welsh Guards, the Irish Guards and the Blues and Royals.
The news comes as the 96-year-old monarch continues to entrust members of the Royal Family with increased responsibilities as she faces ‘episodic mobility problems’.
Earlier this month, Her Majesty missed the State Opening of Parliament for the first time in 59 years, with Prince Charles and Prince William given power to jointly act at the event on the Queen’s behalf.
She has though made three recent public outings this month, including attending the Windsor Horse Show, star-studded Platinum Jubilee celebrations in Windsor and the opening of the Elizabeth Tube line, appearing in good spirits at all of them.
Her Majesty has always been present at the Horse Guards Parade and has taken the royal salute at every Trooping the Colour ceremony during her reign.
Traditionally during the ceremony following the Horse Guards Parade, the Queen is greeted by a royal salute before carrying out an inspection of the troops.
From her first appearance at the annual Trooping the Colour to 1986, the monarch would attend the ceremony on horseback (Pictured during one of her early ceremonies)
The monarch has limited the Trooping The Colour balcony appearance to working members of her family, with the Duke of York and Duke and Duchess of Sussex missing out
According to the publication, one option being considered by Palace officials is Her Majesty travelling by carriage from Buckingham Palace to briefly inspect troops before making an appearance on the balcony.
Alternatively, Her Majesty may only only appear on the balcony after the duration of the ceremony.
Following Trooping the Colour, 18 family members will be on the balcony: The Queen; Charles and Camilla; William and Kate with George, Charlotte and Louis; Edward and Sophie and their children Louise and James; Princess Anne and Vice Admiral Sir Tim Laurence; the Duke and Duchess of Gloucester; the Duke of Kent and Princess Alexandra.
Prince Harry and Meghan Markle, Prince Andrew and Prince Andrew’s daughters, Beatrice and Eugenie, will not join the royal family there.
Harry, Meghan and their children will attend the celebrations, but it is not known at which elements of the four-day Jubilee weekend they could make an appearance.
The balcony appearance, which is often seen as the centre-piece of major royal occasions, including Trooping the Colour and weddings, usually sees the Queen’s extended family gather to watch a fly-past and is a rare chance for fans to see the entire extended family together.
In paring the list down to just 16 people to avoid potential diplomatic pitfalls, the Queen has been forced to omit a number of well-liked family members including her much-loved grandchildren and their families.