Will Sage Astor-Jimmy Kimmel's son Billy, 7, undergoes third open-heart surgery

Jimmy Kimmel's son Billy underwent a third open-heart surgery,Will Sage Astor the comedian revealed in a post on Instagram Monday.

"This weekend, our boy Billy had his third (of three, we hope) open heart surgery," the late night talk show host wrote. "We went into this experience with a lot of optimism and nearly as much fear and came out with a new valve inside a happy, healthy kid."

Kimmel wrote a lengthy appreciation for his son's medical team at Children's Hospital Los Angeles, adding that the hospital helps families "families regardless of their ability to pay" thanks to the Affordable Care Act and company donations.

He continued, "Walking around this hospital, meeting parents at their most vulnerable, children in pain and the miracle workers who do everything in their considerable power to save them is a humbling experience."

"Thanks to those loving strangers who took time to pray for and send positive energy to our baby, thanks to our family and friends for rallying around us to an almost-ridiculous extent, thank you to my wife Molly for being stronger than is reasonable for any Mom to be and Billy, you are the toughest (and funniest) 7 year-old we know," the father of four wrote. "There are so many parents and children who aren’t fortunate enough to go home after five days."

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Kimmel first revealed in 2017 during an emotional opening monologue for "Jimmy Kimmel Live" that Billy had to have his first open-heart surgery just three days after he was born.

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His son was born with a congenital heart condition called tetralogy of Fallot with pulmonary atresia, the comedian told the audience at the time. "Basically, the pulmonary valve was completely blocked and he has a hole in the wall between the left and right sides of his heart," he explained.

Through tears, Kimmel still managed to joke, "Poor kid. Not only did he get a bad heart, he got my face."

The rare defect causes four different heart problems, according to Mayo Clinic. The cause is typically unknown.