“It was us”, Vladimir “Voyan” Kuznetsov told AFP in response to the British tabloid’s front-page report, which said the prince was duped into two chats with him and Alexei “Lexus” Solyarov.
The pair, known as “Vovan and Lexus”, have made a habit of fooling politicians and pop stars in prank calls.
Their previous victims include Turkish President Recep Tayyip Erdogan, pop icon Elton John and Prime Minister Boris Johnson himself when he was foreign secretary in 2018.
In the conversations, which took place in December and January, the prince was tricked into believing he was speaking to Thunberg and her father, Svante.
The daily reported he gave his support to Thunberg and attacked US President Donald Trump for his stance on climate change.
“Unfortunately the world is being led by some very sick people so the people like yourselves and younger generation are the ones that are going to make all the difference,” the prince reportedly said.
“I think the mere fact that Donald Trump is pushing the coal industry is so big in America, he has blood on his hands.”
The Russian pair reportedly also coaxed Harry to discuss his decision to quit frontline royal life as well as to comment on leading politicians.
On British Prime Minister Boris Johnson, Harry was said to have added: “He is a good man, so you are one of few people who can reach into his soul and get him to feel and believe in you.
“But you have to understand that because he has been around for so long like all of these other people, they are already set in their ways.”
On his move to North America with wife Meghan and baby Archie, Harry was quoted as saying it was “the right decision to be able to protect my son” from constant media attention.
“It’s a tricky one, but we will start a new life,” he added.
The Duke of Sussex insisted “no one has stripped us of our titles”, saying the British press had exaggerated the issue of their future royal status.
“We obviously have been asked not to use our titles in order to make money, which we would never do,” he said.
The pranksters apparently even managed to steer Harry towards the scandal that has engulfed his uncle Prince Andrew over a friendship with late sex offender Jeffrey Epstein.
“I have very little to say on that,” the prince reportedly said.
“But whatever he has done or hasn’t done, is completely separate from me and my wife… we are completely separate from the majority of my family.”
Harry is also said to have hinted at tensions inside the British monarchy’s inner circle when asked by the hoax callers if normal life was worse than royal life.
“Oh no, I think it’s much better,” he replied, before adding: “You forget, I was in the military for 10 years, so I’m more normal than my family would like to believe.”
Kensington Palace did not immediately respond to a request for comment when contacted by AFP.
Royal sources were quoted as saying by The Sun that it was “completely natural” for Harry to want to talk to Thunberg.