Letters from Hunter's abandoned laptop show the Fox anchor and the president's son were in contact until around 2015 – showing Carlson failed to assert the true nature of his friends throughout his full coverage of the scandals regarding Hunter's business and personal transgressions revealed by his abandoned computer.
In emails, Hunter declared his "love" for Carlson and his family, called him "buddy" and told him "you're a friend".
A Fox News spokeswoman said Carlson "has been transparent about his relationship" with the president’s son.
In August 2015 data on the 30 million users of extramarital affairs website Ashley Madison were leaked, including Hunter's name and credit card.
DailyMail.com wrote a story about Joe Biden's son's claimed use of the site, whose tagline is "Life is short. Have an affair".
On August 27, Hunter wrote "call me pls" to the top Fox anchor. About two hours later Carlson wrote back explaining he had intervened in their reporting on Hunter's behalf.
"Just lost my s**t on the editor over there. He claims the London office forced him to do it. He's a pig either way, and I told him so," he said.
"This whole thing is disgusting and awful and it breaks my heart that you all have to go through it. I'm really sorry. Let me know if there's anything [Carlson's wife] Susie and I can do to help."
Hunter wrote back: "I'm sorry for even calling you. I know I put you in a difficult position- and upon reflection, as you're [a] friend I should have never done that.
"I was just so upset that they went to my house and confronted Finnegan. I've been in DE [Delaware] the last two months sleeping in my nephew's bed, and it's hard to even get up in the morning sometimes.
"Eric [Schwerin, Hunter's business partner] provided all the information on background that proves this was not me - not my IP address- not my credit card #, not my birth date etc...but they still come anyway. I can take the hit- I'll be fine, but the notion that under any circumstance whether ordered to by an editor or not that someone would confront my 16-year-old daughter at my home is just wrong.
"Regardless, I should have never put you in this position- you have your own family all of whom I love, and your own business and defending me is not something a friend should ask a friend to do. Tell Susie we love her and miss you both very much."