Mills was born in Hammersmith, London, England on 18 January 1973. His mother, Hayley Mills, had made her name as a child star in the 1960s, and met Mills' father, Roy Boulting, on the set of light British comedy The Family Way. At the time, Boulting was still married to his third wife Sandra. Boulting was 33 years Hayley Mills' senior, and only five years younger than her father, Sir John Mills. The pair went on to marry in 1971. The family lived on Belgrade Road, in the south-west London district of Hampton, and had an additional seat at Cobstone Windmill at Ibstone, Buckinghamshire. The marriage did not last, and the pair split in 1975, followed by an official divorce in 1977. At this point, Hayley was pregnant again by actor Leigh Lawson with her second son, Jason. Mills did not see his father again until he was 16.