The 'What's Love Got to Do with It' hitmaker will marry Bach at their home in Switzerland on July 21, reported Ace Showbiz.
Italian fashion designer Giorgio Armani is expected to attend the wedding.
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Turner, 73, first met Bach, who is 16 years her junior, when he worked as a record producer at EMI. They started dating in 1990s.
The couple has been living together at their Switzerland home for more than 15 years.
This marriage will be the second marriage for the singer, who was married to Ike Turner from 1962 to 1978. She left him after suffering from years of abuse.