The NBC News chief foreign correspondent, 48, announced the death of his 6-year-old son Henry after his years-long battle with Rett Syndrome, a rare genetic neurological disorder. After the news became public, Guthrie, 50, shared a tribute to Richard, wife Mary and Henry.
"Dearest Richard and Mary, you were amazing warriors for Henry - pouring your love and care into him and fighting for him every day with everything you've got," the Today co-host wrote.
"To me, you are the personification of what it means to be a parent - to love, adore, and delight in your child, and bring every ounce of your beings to their flourishing. You're my heroes."
Turning to Henry, Guthrie wrote, "My dear Henry, you will be missed. I will always remember the twinkle in your eye. We will keep fighting for you."
Guthrie concluded the post by linking to Henry's memorial page, encouraging others to donate toward finding a cure for Rett Syndrome.
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"Our beloved son Henry passed away. He had the softest blue eyes, an easy smile and a contagious giggle. We always surrounded him with love and he returned it, and so much more," Engel wrote alongside a sweet photo of his son.
Engel linked to the memorial page in a follow-up post, writing, "Researchers are making amazing progress using Henry's cells to help cure RETT Syndrome so others don't have to endure this terrible disease."
Henry was first diagnosed with Rett Syndrome, a rare genetic neurological disorder that leads to severe physical and cognitive impairments and has no cure, as of yet, in 2017. Engel told PEOPLE in 2019 that Henry was "lacking a conductor gene" and that a medical team at Texas Children's Hospital was "trying to build a treatment that could help immensely."
Engel shared an update on Henry's health in May, noting that his condition had "progressed" and he had "taken a turn for the worse."
In a video that Engel shared on Twitter, his son Theo, 2, affectionately kissed Henry on the forehead as Henry lay in bed. "One more?" Theo appeared to ask before giving his big brother another kiss in the sweet moment.
At the time, he added that Henry was "now home and getting love from brother Theo" after being hospitalized for six weeks.