Tatjana, 17, flew from her family home in Spain to sing for the judges, who were amazed to discover she was related to the 72-year-old, whose hits include Big Spender, Goldfinger and Diamonds are Forever.
But despite expectations, when the teenager opened her mouth to sing, sources close to the show said that judges were not blown away by her rendition of Faith Hill's song There You'll Be.
This left them with a big dilemma over whether to put the curly-haired youngster through.
The hopeful is the daughter of Bassey's adopted son Mark Novak.
Her parents split up in the early 1990s and Tatjana explained to judges that she had not seen her superstar gran since she was a little girl.
ITV has not yet set a firm date to screen the audition, which took place in Birmingham.
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