The lorry driver involved in the accident has been taken to hospital, in addition to an elderly man who was hospitalised with a leg injury.
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Joshua beat the older, more experienced boxer in front of 90,000 fans in Wembley Stadium.
Dry for most of the night. Rain in the southwest by dawn.
Host Paddy McGuinness tweeted a tribute to contestant Charlie Watkins whose date was featured in Saturday's episode.