A member of the Army has passed out during a rehearsal on the Mall near Buckingham Palace, ahead of the official Japanese state visit to the UK on Tuesday.
Images show a Foot Guard lying motionless on the ground during rehearsals, before he is helped and led away.
It comes as temperatures in London reached almost 30C (86F) on Monday.
The Army said it does not comment on individual cases but the man received appropriate medical treatment.
The Army posted on X saying more than 1250 soldiers from the Household Division – including 250 Army musicians, 9 regiments and more than 240 military horses – were involved in activities.
The official three-day state visit, which is hosted by King Charles, begins on Tuesday.