From Wiki:
"Simon was born in July 2003 to Lucy Richards, who had already split up with Peter. On learning that he had married his girlfriend, Shelley, when they had married first - she told Shelley that her marriage was illegal. In revenge, Lucy tricked Peter into thinking they had a future together, then, in front of pub regulars, announced she and Simon were emigrating to Australia. Peter resigned himself to the fact that he would never know his son, and left the Street soon after.
Peter was given custody of Simon when Lucy died of cancer in 2008 and they moved in with Peter's father, Ken (William Roache) and his wife Deirdre (Anne Kirkbride)....