ill Roache's eldest daughter Vanya died from liver failure.
The "Coronation Street" actor is currently on compassionate leave from the soap - in which he plays Ken Barlow - after his 50-year-old daughter, whom he had with his first wife Anna Cropper, passed away after she developed the life-threatening condition.
Vanya's partner Toby Evans told the Daily Mirror newspaper: "Vanya was a nice person, a lovely person. It was liver failure that she died of. It happened very quickly."
This is the third family loss for Bill as his second wife Sara Mottram died in 2009 aged 58 and their daughter Edwina passed away from pneumonia at the age of 18 months.
A source said: "Bill is utterly heartbroken. No father should have to go through the loss of a child, let alone two. ITV are giving him all the time he needs but he's understandably very upset. After hearing the news on Friday he's been told to take as long as required. There's no word just yet on when he'll return."
Vanya leaves behind fiancé Toby, who she lived with in Chichester, West Sussex, and friends of iconic actor's daughter have already begun to pay respects on social media.
Her friend Wendy Elisabeth Vick posted a picture of the pair of them with the caption: "My beautiful, perfect, wonderful best friend and soulmate. Forever in my heart."
At the time of writing, Bill or the rest of his family - including other daughter Verity and two son Linus and James - have yet to make a statement on the tragic news.