Billy Platt was the son of Sarah Platt and Todd Grimshaw, who was born three months prematurely on 31st May 2004 by caesarean section at Weatherfield General. Sarah had recently split up with Todd after discovering he was gay, but all the stress caused her to suffer a placental abruption which made her to go into labour prematurely. Billy was transferred immediately to an incubator, but died on 1st June 2004 from surfactant deficient lung disease. Todd never saw his son alive as Sarah refused to give him access although Sarah's mother Gail Platt gave him a photograph. Neither his birth nor death were registered with a first name as Sarah changed her mind about the name she and Todd had picked for the baby. Billy's funeral was held on 7th June, which both the Platts and Grimshaws attended; even after Sarah had barred Todd from attending Billy's funeral. Most of the other Street residents agreed that he was to blame for Billy's death, and thought it was best that Todd kept a low profile. Sarah's stepfather Martin bought the headstone to put on the baby's grave.
Billy's death was still remembered in sorrow many years later. In 2013, Gail and Nick Tilsley were still bitter towards Todd, blaming him for Billy's death even almost a decade later. However, Sarah held no bad feelings towards Todd, and they reminisced like old friends upon her return to Weatherfield from Milan in March 2015.