A body, believed to be that of the wife of Tetra Pak heir Hans Rausing, has been found in a flat in Belgravia, London.
Police say they are treating Eva Rausing's death as "unexplained".
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The man, who was in his 30s, has not been identified, while several other people are believed to have suffered serious injuries.
The Olympian was one of several sports stars who opened up to the prince during an event for his mental health charity Heads Together.
There will be sunny spells, with temperatures peaking at 23 Celsius (73F). However, Northern Ireland will experience frequent showers.