A Metropolitan Police spokesman said the arrests were made over alleged public order offences.
Six males were arrested during the game at Millwall in relation to a banner being unfurled at the game. They remain in custody at this time."
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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.