The actor announced the news with a photo of Thing One and Thing Two from "The Cat in the Hat."
"Danneel, JJ and I are excited to announce the birth of our twins Zeppelin Bram and Arrow Rhodes. They were born early yesterday morning. Everyone is doing great! #twinning," he wrote at the time.
Ackles and Harris married in 2010 and welcomed Justice in May 2013. The actor admitted in an interview with E! News after Justice's birth that becoming a father was "quite the adjustment."
"A friend of mine says it's a slightly different gear, and I said, 'Different gear? No, you put it in park, you get out of the car, you get in a different car, you take a left down a wrong street.' That's basically where I'm at now," he confessed.
"I'm lost, I'm just completely lost ... but the baby's doing great," the star said.
Ackles plays Dean Winchester on "Supernatural," which airs Thursdays at 9 p.m. ET.
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