The band's drummer Chad Smith admitted the 'By The Way' hitmakers are "psyched" to have reunited with the guitarist, who initially joined the group in 1988, and confirmed they are currently "concentrating on new songs and writing a new record".
He said: "Yes, John is back in the band, and everyone knows that. We’re psyched. The festivals are the only shows booked. For now, we’ll mostly be concentrating on new songs and writing a new record.
"We’re all real excited to make new music."
When asked to clarify the band are in the middle of making a new record, he told Rolling Stone magazine: "Yes. That’s all I can say."
John's return meant the Chilis parted ways with long-serving guitarist Josh Klinghoffer, who they hailed as a "beautiful musician".
In a statement posted on their Instagram Story in December, the group wrote: "The Red Hot Chili Peppers announce that we are parting ways with our guitarist of the past ten years, Josh Klinghoffer.
"Josh is a beautiful musician who we respect and love.
"We are deeply grateful for our time with him, and the countless gifts he shared with us.
"We also announce, with great excitement and full hearts, that John Frusciante is rejoining our group."
This is the third time John has returned to the band, as he first left in 1992 to enter rehab for his drug addiction, before returning in 1998 until 2008, although his official exit was confirmed a year later.
Explaining his decision to depart the group, who were on a break anyway at the time, the 49-year-old musician said in 2009: "When I quit the band, over a year ago, we were on an indefinite hiatus.
"There was no drama or anger involved, and the other guys were very understanding.
"They are supportive of me doing whatever makes me happy and that goes both ways.
"To put it simply, my musical interests have led me in a different direction."
He was just 18 when he joined the US band, and he took the place of the late Hillel Slovak, who suffered a heroin overdose.
The last RHCP's record Frusciante featured on was 2006's 'Stadium Arcadium'.