Her Majesty, wearing a silk headscarf and pea green overcoat, was all smiles as she laughed with the King of Bahrain.
The 91-year-old monarch grinned and pointed her fingers outward in a light-hearted gesture as she stood alongside Hamad bin Isa Al Khalifa on the third day of the event.
The Gulf state ruler was also seen laughing heartily alongside Prince Andrew, the Duke of York.
It is little surprise the Queen was in high spirits after her horse Barber’s Shop won the RoR Tattersalls Thoroughbred Ridden Show Series prize for the third year yesterday.
And she collected a small trophy after rider Katie Jerram guided the horses to success in the showing category, where a horse’s physique, movement and appearance are assessed by judges.
The Duke of Edinburgh, who last week announced his retirement from public engagements, also put in an appearence.
He was seen steering a horse-drawn carriage across the grounds, carrying a whip in one hand and the reins in the other.
The Royal Windsor Horse Show is said to be the Queen’s favourite equestrian event, held in what is esentially her own back garden of Royal Windsor Park.
The five day-event is the UK’s largest outdoor horse show, with international competitions in a variety of disciplines, including jumping, dressage, endurance and showing.
Now in its 72nd year, the gala was launched in 1943 as a fundraiser for the war effort.
The Queen has attended every single year of the events history, and even competed in her younger years, alongside husband Prince Philip.