Three British soldiers fainted during the final rehearsal for the annual Trooping the Colour parade in front of Prince William amid the scorching London heat, the reports said.
The reports said the soldiers were wearing woollen tunics and bearskin hats in the nearly 30-degree Celsius London temperature.
The temperature in London on Saturday was due to hit 30 C (86 F).
Prince William in a tweet, wrote, "A big thank you to every soldier who took part in the Colonel's Review this morning in the heat. Difficult conditions but you all did a really good job. Thank you. W"
In a follow-up tweet, he wrote, "The hard work and preparation that goes into an event like this is a credit to all involved, especially in today's conditions."
The reports said a military trombonist who fainted got up again in an attempt to continue to play. Moments later medics rushed to help him, the reports mentioned.
The UK Health Security Agency has issued a hot weather alert for South England, BBC News reported.
The event was a rehearsal for Trooping the Colour, an annual military parade held each June to mark the monarch's official birthday. King Charles III will oversee the ceremony on June 17.
