Sarah Ferguson landed in Jodhpur from Delhi amidst tight security, to attend the lavish birthday party being organised by Naomi Campbell for her Russian billionaire boyfriend Vladimir Doronin.
Ferguson, 53, and Campbell, 42, are long-time friends and have holidayed together before.
An onlooker also claimed to have seen music producer Quincy Jones arriving at Jodhpur Civil Airport shortly before the duchess arrived, the Daily Mail reported.
Ferguson had been in Delhi to raise funds for the Indian Head Injuries Foundation (IHIF) at the Delhi Commonwealth Women's Association (DCWA) in Zamrudpur.
Thirteen chartered planes are believed to have ferried around 200 guests to India from far afield as Moscow, London, New York, Abu Dhabi, Istanbul, Mumbai and Delhi ahead of the party at the 15th century majestic Mehrangarh Fort on Wednesday.
The guests will be staying at the stunning Umaid Palace Hotel, where a two-night stay costs more than 1700 dollars.
Campbell has reportedly splashed out 500,000 dollars to fly Diana Ross to India to perform at the party.
The supermodel arrived in India with Union Minister Praful Patel's daughter Purna to oversee the preparations.
The main bash will be held at the fort, which will be entirely lit up with royal oil lamps rather than electrical lights. (ANI)