"Growing Pains" star Jeremy Miller opened up about his life-long struggle with alcohol addiction.

The child actor revealed on "Oprah: Where Are They Now?" that he began drinking at age 4.

"I began drinking at 4 years old," Miller said on "Oprah: Where Are They Now?" "My grandparents used to throw a lot of parties, and I would run around after the parties and finish off all the empty beers."

But it wasn't until he was 12 that he "got hammered."

"I didn't really mess around with it after that until I was around 12," he says. "That was the first time I ever got hammered."

Miller explained that he believes there was just "something there" that caused him to drink.

"There was always something there, whether it's genetic component, mental, whatever you want to call it. There was something there. I never had that 'off' switch," Miller says.

The actor, 39, finally hit rock bottom when he woke up from a night of drinking and his fiancée told him that he drove his car while drunk.

"Rock bottom for me was waking up after having been completely blacked out, not having a clue what I did, with my fiancée sitting on the end of the bed, yet again, pissed and [me] not knowing what she could say. She could have told me I got in the car and killed four people last night; I would have had no clue," Miller says. "That was my rock bottom."

Catch more of Miller's interview on "Oprah: Where Are They Now?" on Jan. 30 on OWN.