Born Kelly Ann Parsons on November 23, 1979, in Rochester, Kent, she is the daughter of Sandra, a cook, and Ken, a scaffolder. Ken Parsons died from cancer in November 2007, during Brook's time on Strictly Come Dancing.
Kelly attended The Thomas Aveling School in Warren Wood, Rochester, Kent. After leaving school in Rochester, Brook studied at the Italia Conti stage school in London for three years before becoming a professional model.
