The Hollywood star - famous for roles in The Fresh Prince of Bel-Air and Men in Black - met students at St Martin-in-the-Fields High School for Girls in Tulse Hill, doing a question and answer session and signing autographs.
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Police were called to Kilburn High Road at 5.20pm after reports of a shooting.
In just 24 hours the offer was retweeted more than a thousand times on Twitter.
What a year it's been full of ups and down, turmoil and change and it seems events here in London have got the entire nation talking.