Police have confirmed a football fan died on Tuesday evening following an assault before England's Euro 2012 qualifier against Wales at Wembley.
The victim, in his 40s, suffered a heart attack at Wembley Stadium, in North London, before he was rushed to hospital with head injuries. He is understood to have been a Wales supporter.
Six suspects have been arrested, all of whom are understood to support the away team, a Scotland Yard spokesman said.
Emergency services were called to an area outside the ground at around 7.20pm, following reports of an assault shortly before kick-off.
A London Ambulance Service (LAS) spokesman said: "I can confirm that LAS got a call at 7.20pm to reports of an assault outside Wembley Stadium.
"Staff treated a 44-year-old man who had suffered a cardiac arrest. Extensive efforts were made to resuscitate the patient and he was taken to hospital."
Staff on stand-by at the international match, which England won 1-0, were on the scene within three minutes, the spokesman said.
The victim was taken to a North London hospital in an ambulance belonging to a private medical contractor employed by Wembley. He was pronounced dead at 8.50pm.
A post-mortem examination will be arranged in due course.
Police believe they have identified the victim but await formal confirmation that all his next of kin have been informed.
Officers from the Met's Homicide and Serious Crime Command are now investigating his death.
The married man's relatives were being informed of his death.
Cardiff have confirmed the victim was a supporter of the Championship club and issued a statement on their official website which read: "Late on Tuesday night, details reached us concerning a tragedy where a Wales and Cardiff City supporter died at the match between England and Wales.
"Out of respect for the family of the supporter, the sensitivity of the situation and until full details and circumstances are ascertained, no statements will be made until deemed fit by the proper channels."