Eric Roberts admits the "toughest" time in his life was losing his relationship with his daughter Emma Roberts

Eric admits becoming a grandfather made him realise just how much he has lost out on with his own daughter.

The 68-year-old actor - who has two grandchildren from his stepchildren, while Emma has three-year-old son Rhodes - was asked on the 'Inside of You' podcast what the hardest part of his life has been, to which he replied: "Probably the loss of relationship with my daughter

"There's not a pain, there's a sadness for the, most likely, misunderstandings we'll all have forever. Because we're human."

Eric says his eldest grandchild "looks like" the 'American Horror Story' actress and "reminds me of what I didn't have."

He said: "I started accepting that about myself with the birth of my grandchildren.

"Especially the five-year-old, she was first and she was a girl and took a liking to me in a very strong way."

The 'Runaway Train' actor details their estrangement in his recently released memoir, 'Runaway Train: Or the Story of My Life So Far'.

And he admitted the chapter was "the most painful personally" to write, despite earlier admitting he felt "sadness" not "pain".

He said of the tell-all: "To write it at all was the hardest thing to write.

"That book was hard to write and I didn't want to write it."

In the tome, he writes: "Of course, the biggest consequence of my drug use was losing Emma."

He also acknowledged the impact his addiction had on his relationships with his sisters Julia and Lisa Roberts.

He added: "I wouldn't be surprised if they suffered from PTSD from when it was dangerous to be around me.

"Lisa and Julia needed love and protection - instead they got fear and uncertainty."

At the time of his breakup from Kelly, his estranged sister Julia took his ex's side in the legal case because of his addiction issues.

While he doesn't go into detail in the book, he has admitted he now realises it was the right decision.

He added: "I imagine I will remain as Julia's brother and Emma Roberts' dad for the rest of my life.

"I'd like to make good on that, to move aside proudly and with grace. That's part of the reason for writing the book."

Eric - who married Eliza Garrett since 1992 - has been open about his own difficult childhood, describing his father Walter Roberts as a man who drank and would have violent outbursts, having also been raised by an abusive father.

He said his dad was jealous of his career and "was a very screwed-up individual and not safe for me, or anyone, to have as a father".

Now, he feels he has come to terms with his own father, and the shame he felt seeing some of his dad in himself.

He wrote: "I knew that I loved him. I couldn't live down the shame of loving him or of who he was, someone capable of terrible things.

"I was ashamed of being so much of him and so much like him... If you've ever loved a parent ... with a cruel nature, it's never too late to begin to recover from the shame and pain of it all."