Is Slavomir Rawicz's story true?

It’s an obviously fictional story. Its the fucking Himalayas we are talking about.

Ben, I think I know who your princess was. Her name was Princess Barbara Mikhailovna Cantacuzène and she was a great-granddaughter of Ulysses S. Grant.

From Wikipedia Julia Grant Cantacuzène - Wikipedia

“Princess Barbara Mikhailovna Cantacuzène, Countess Spiransky (b. 27 March 1904, St. Petersburg, d. 1991) married firstly Bruce Smith, secondly William Durrell Siebern. She was known as Bertha. She had a son by her first husband, named Bruce Smith, as well.”