At a dress rehearsal for the birthday parade for King Charles III. several soldiers fainted briefly in London. The heat of around 30 degrees Celsius, which prevailed in London over the weekend, apparently bothered them on Saturday.

British media footage showed one of the unconscious men dutifully holding onto his trombone before he was able to get himself up. At least three soldiers fainted and were taken on stretchers while two others needed help exiting the parade ground, the PA news agency reported.

Prince William, who inspected the parade on horseback at Horse Guards Parade, thanked those involved for their perseverance in the heat. “Difficult conditions but you all did a really good job,” wrote the heir to the throne on Twitter.

The birthday parade “Trooping the Color” will take place next Saturday in honor of the king. It is traditionally held in June, and thousands of onlookers are expected in London. Charles’ actual birthday is in November.