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 2nd June 2004. Todd never saw his child alive as Sarah refused to give him access although Sarah's mother Gail Platt gave him a picture of his son. Billy's funeral was held on 7th June, which the Platts and Grimshaws attended, even after Sarah had banned 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 felt after many years. In 2013, Gail and Nick Tilsley were still bitter towards Todd, blaming him for Billy's death even almost ten years later. However Sarah held no bad feelings towards Todd, and they caught up like old friends upon her return to Weatherfield in March 2015.