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Over 20,000 people are expected to descend on Trafalgar Square to celebrate the nation's patron saint.
The heart of the capital will be fluttering with flags for a packed afternoon of family activities, live music and entertainment on the stage, with lots of stalls selling traditional English food like fish and chips, warm ale and sweet treats.
The main stage is always hosted by a well-known celebrity (last year it was TV and Heart radio presenter Zoe Hardman) who will be introducing some live music, comedy and dance acts.
You'll also be able to try out lots of fun activities like the Silent Disco -- where you hire a pair of headphones and dance around to the sounds playing inside your ears -- and science workshops, sports activities, races and face painting for the kids... and maybe even a chance to get a selfie with a dragon.
And it wouldn't be St. George's Day without a bit of Morris dancing and an appearance by the Pearly Kings & Queens!
