The multi-faceted restaurant and bar on Portobello Road is understood to have shut its doors a couple of months ago, but Denney has only now confirmed the closure.
"We have had to make a really tough decision; it has been an incredibly challenging year," says Denney, in a statement provided to BigHospitality.
"The support we have had from our immediate locals has been immense but sadly not enough to sustain the business long term."
Fiend opened in July last year in the space that was once home to well-regarded Mexican restaurant Santo, and marked Denney's return to Notting Hill following the closure of his popular 108 Garage restaurant in 2019.
It received rave reviews upon its launch, with The Guardian restaurant critic Grace Dent calling it 'clever, deliciously erratic and slightly bewildering'.
In an interview with BigHospitality at the time, Denney described it as a 'more grown-up restaurant' compared to his previous ventures.
"It is with great sadness we have had to make this decision," adds Denney, on the closure.
"A huge thank you to all involved for your tireless dedication."