Emirati Princess Latifa Al Maktoum has urged British police to reinvestigate the disappearance of her older sister, Princess Shamsa.
Princess Latifa, who says she has been held captive in a "villa jail" in Dubai by her father Sheikh Mohammed bin Rashid Al Maktoum since an attempt to flee in 2018, alleges that Shamsa was also captured by her father.
Shamsa, now 38, was abducted from the streets of Cambridge on 19 August 2000 and has not been seen in public since. It is believed she was returned to the United Arab Emirates.
Cambridgeshire Police previously confirmed "aspects" of its 2001 investigation, which found insufficient evidence to take any action, will be revisited, although the force insisted the investigation was no longer "active".
In a letter from Latifa to the force, obtained by the BBC, she wrote: "All I ask of you is to please give attention on her case because it could get her her freedom … your help and attention on her case could free her.
"She has strong links to England … she really loves England, all of her fondest memories are of her time there."
Footage filmed by Latifa of her life in the "villa jail" was broadcast this month and was described by UK Foreign Secretary Dominic Raab as "very distressing", and triggered worried responses around the globe.
But a family statement released through the UAE embassy in London downplayed allegations of mistreatment, and said she was being cared for at home.
It said: "She continues to improve and we are hopeful she will return to public life at the appropriate time."