She is reported to be Yelizaveta Vladimirovna, a 17-year-old born of a years-long affair between Putin and her mother Svetlana Krivonogikh.
Sources who spoke to investigative site
Putin, who is notoriously tight-lipped about his family, offered no reaction to the report and Kremlin spokesman Dmitry Peskov denied all knowledge of Svetlana or her daughter.
Vladimir Putin reportedly has a secret teenager daughter with cleaner-turned-millionaire Svetlana Krivonogikh, who he reportedly had an affair with starting in the late Nineties
Information gathered by Proekt suggests Svetlana was born in St Petersburg in 1975, growing up in a modest apartment amid neighbours with links to organised crime.
During the late 90s she worked as a cleaning lady at store close to her family home while studying at the University of Economics and Finance in the Department of International Economic Relations.
In 2000 she received her diploma, and soon after moved out of the apartment and into her new residence on the Kamenny Islands with her mother.
Apartments on the island are not for general sale and are occupied solely by those close to Putin, the site reports.
Around the same time she is thought to have come into ownership of valuable stock options, with no benefactor listed on public records.
Putin is thought to have two daughters by his ex-wife, including dancer-turned-political appointee Katerina Tikhonova
However, one of her biggest stock holdings is in Bank Rossiya, which has ties to Putin and many of his cronies.
Three years later, Svetlana gave birth to daughter Yelizaveta – who does not have a father listed on her birth certificate, according to Proekt.
The only potential identifier is her middle name – typically derived from the father’s name in Russia – which is Vladimirovna, the site reports.
Two sources close to Svetlana said Putin was her mystery benefactor, and that their relationship began some time in the Nineties and ended in the early 2000s.
It is not clear exactly when or how the pair met, or why they eventually split up.
Some time before 2010 the two are thought to have severed ties completely, the sources said.
However, Svetlana still enjoys her house in St Petersburg along with other properties in Sochi and Moscow, worth an estimated total of $11million.
She is also thought to own a majority stake in the Igora Ski Resort, 70 miles north of St Petersburg, which is a favourite haunt of Putin’s, and another majority stake in the Leningrad Center performance venue.
According to Proekt, daughter Yelizaveta uses a fake surname and has several social media profiles under that name.
Images collected of her from those accounts have ‘a phenomenal resemblance’ to Putin, the site reported.
Doctor Maria Vorontsova is thought to be Putin’s second daughter by his ex-wife, though he has never publicly acknowledged either of the women
Putin was married to wife Lyudmila Aleksandrovna Ocheretnaya from 1983 until they divorced 2013, and the pair are thought to have two daughters together.
One is Katerina Tikhonova, a dancer-turned-political appointee, and the other is doctor Maria Vorontsova.
However, Putin has never publicly acknowledged the women as his daughters, and is typically tight-lipped about his family.
He is now thought to be dating former gymnast Alina Kabaeva, 37.
Proekt say they contacted Svetlana who promised to return their call – but had not heard from her at the time of publication.
Yelizaveta deleted photos displaying her face from social media after Svetlana was contacted and prior to publication of the story, the site added.