In April 2016, comedian Patton Oswalt lost his wife Michelle McNamara unexpectedly when she passed away in her sleep at the age of 46. Almost a year after that, Oswalt has opened up about the heartbreaking cause that led to the death of the mother of his child.

"We learned today the combination of drugs in Michelle's system, along with a condition we were unaware of, proved lethal," the American actor revealed in a statement to the Associated Press.

He further explained that "blockages [in her arteries], combined with her taking the medications Adderall, Xanax and the pain medication fentanyl" caused her sudden death.

Both Oswalt and his wife had "no idea" that Michelle was suffering from a condition that caused blockages in her arteries, as per reports.

In a previous interview with the New York Times, The King of Queens star had explained his fears that his wife might have accidentally overdosed. Recalling the tragic night with his wife and the founder of True Crime Diary website, Oswalt had said, "I have a feeling it might have been an overdose. That's what the paramedics there were saying while I was screaming and throwing up."

As it turns out, Michelle – who was writing a book about a serial rapist and killer at the time – was stressed and unable to sleep at night. On 21 April, Michelle reportedly took some Xanax before hitting the bed, and she never woke up.

After her death it's now upon Oswalt to raise their 7-year-old daughter Alice. The single father even penned an emotional essay for GQ as he explained his first year of solo parenting.

He wrote, "I've missed forms for school. I've forgotten to stock the fridge with food she likes. I've run out of socks for her. I've run out of socks for me. It sucked and it was a hassle every time, but the world kept turning. I said, 'Whoops, my bad,' and fixed it and kept stumbling forward."

However, the comedian ended his touching essay on a hopeful note as he reminded fellow single parents to "keep going forward, looking stupid and clumsy and inexperienced at first, then eventually getting it."