No one has ever challenged it except Prof. P. N. Oak, who believes the whole world has been duped. In his book Taj Mahal: The True Story, Oak says the Taj Mahal is not Queen Mumtaz's tomb but an ancient Hindu temple palace of Lord Shiva (then known as Tejo Mahalaya). In the course of his research Oak discovered that the Shiva temple palace was usurped by Shah Jahan from then Maharaja of Jaipur, Jai Singh. In his own court chronicle, Badshahnama, Shah Jahan admits that an exceptionally beautiful grand mansion in Agra was taken from Jai SIngh for Mumtaz's burial.
Oak's inquiries began with the name of Taj Mahal. He says the term "Mahal" has never been used for a building in any Muslim countries from Afghanisthan to Algeria. "The unusual explanation that the term Taj Mahal derives from Mumtaz Mahal was illogical in at least two respects.
Firstly, her name was never Mumtaz Mahal but Mumtaz-ul-Zamani, Secondly, one cannot omit the first three letters 'Mum' from a woman's name to derive the remainder as the name for the building. Taj Mahal, he claims, is a corrupt version of Tejo Mahalaya, or Lord Shiva's Palace. Oak also says the love story of Mumtaz and Shah Jahan is a fairy tale created by court sycophants, blundering historians and sloppy archaeologists. Not a single royal chronicle of Shah Jahan's time corroborates the love story. Prof. Oak points out a number of design and architectural inconsistencies that support the belief of the Taj Mahal being a typical Hindu temple rather than a mausoleum.