In 1596, while writing the history play King John, Shakespeare's 11 year old son, Hamnet, died of the plague.
Shakespeare's grief can be seen in the play. In the words of Constance, mother of Prince Arthur, who, believing him to be dead says;
"Grief fills the room up of my absent child.
Lies in his bed, walks up and down with me.
Puts on his pretty looks, repeats his words.
Remembers me of all his gracious parts.
Stuffs out his vacant garments with his form.
Then, have I reason to be fond of grief".
Constance then exits, and from here on is not seen through the rest of the performance.