This child was the miscarried son of Robert and Cora Crawley, the Earl and Countess of Grantham. He was miscarried after Cora slipped on a piece of soap she had dropped on the floor. Her maid, Sarah O'Brien, believing she was due to be sacked, deliberately left half of the soap on the floor, so that Cora would fall and miscarry; having a change of heart at the last minute, O'Brien changed her mind but it was too late and Cora got out of the bath and slipped on the soap before she could stop her.
If this child had survived he would have been known as Viscount Downton and displaced Matthew Crawley who, after the unfortunate deaths of James and Patrick Crawley on the Titanic, had become heir.
When Robert discovered the child would have been a boy, he was heartbroken.