Alicia Witt's parents' cause of death revealed two months after they were both found dead in their home

The parents of Walking Dead actress Alicia Witt died after "exposure to the cold", their death certificates have revealed.

Witt's mother Diane, 75, and father Robert, 87, were both found dead in December after a welfare check was conducted on their Massachusetts home.

The cause of death was revealed to be "probable cardiac dysrhythmia" due to the cold, according to the death certificates obtained by The Telegram & Gazette.

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Witt announced her parents' shock passing after officers found the couple deceased on December 20 with no obvious causes of death.

"I reached out to a cousin who lives close to my parents to check on them. Sadly, the outcome was unimaginable," Witt said at the time.

"I ask for some privacy at this time to grieve and to wrap my head around this turn of events, and this surreal loss."

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There had been reports the couple had been experiencing furnace problems and were using a space heater, however firefighters did not find any evidence of carbon monoxide in the home.

"There was no trauma," Lieutenant Sean Murtha said in a statement.

Witt opened up about her parents' sudden deaths on January 25 in an emotional post.

"It's been a month since I got scared, not having heard back from them, and called to have them checked on," she wrote on Facebook.

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"Waiting, phone in hand, praying fervently that the next call would be from them, angry I'd gotten someone else involved. Knowing as soon as I heard the detective's voice on the other line that they were gone.

"Knowing I would never hear their voices again. Beginning the rest of my life of finding them on the breeze, in a song, in a dream."

Witt made her acting debut in the 1984 movie Dune and has appeared in television shows including The Walking Dead, Orange is the New Black and Twin Peaks.