Cyclist Joanna Rowsell tweeted a picture of her hat box, as she prepared for today's outing to Buckingham Palace.
The Olympic champion from Sutton said she was "so excited" about the occasion.
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A lamp in the tower which houses Big Ben is to be switched off for the first time in more than 70 years.
Sir Bruce entertained audiences for more than seven decades.
Work in the tower will also pause over the bank holiday weekend.