Google co-founder Larry Page and girlfriend Lucy Southworth on the Google private jet.

Larry Page, Google's billionaire co-founder, is set to marry his girlfriend, Lucy Southworth, on a tiny Caribbean island this weekend, a source familiar with the wedding arrangements said.

The impending nuptials will create an instant billionaire out of Southworth, who will share in Page's estimated $21 billion fortune.

The couple will hold the ceremony on an island enclave owned by Richard Branson, the billionaire owner of Virgin Group, who will act as best man to Larry, the source said.

Page, 34, co-founded the famous search company in 1998 with Stanford University classmate Sergey Brin. The two are now co-presidents of Silicon Valley-based internet leader Google.

Page was best man at Brin's wedding in the Bahamas earlier this year.

The New York Post reported on Wednesday that 600 guests will be flown on private planes to the wedding on Branson's Necker Island. The Post's Page Six column said wedding planners booked up the hotels on the neighboring island of Virgin Gorda six months in advance.

Since 2003, Southworth has been a doctoral student in biomedical informatics at Stanford University. She graduated from the University of Pennsylvania in 2001 and holds a master's of science degree from Oxford University.

Southworth and a Google spokesman did not respond to requests for comment.

Details on the guest list and the exact timing of the wedding were not disclosed by the source.

In early November, Silicon Valley celebrity gossip site valleywag.com reported the two would marry on Branson's Necker Island, which is about a mile from Virgin Gorda in the British Virgin Islands.

Offering accommodations at $US46,000 per night, "Necker Island exudes the elegance and lifestyle of the rich and famous," brags one online reservation site, which says the island has 14 bedrooms and was bought by Branson in the 1970s.

Page and Branson are good friends and Branson enlisted the digital map Google Earth service to help search for his adventurer friend Steve Fossett, whose plane went missing in September.

U2's activist lead singer Bono, along with several billionaires, Silicon Valley technology gurus and college friends from Stanford University are invited, the Post said.

Since the firm went public in 2004, its stock has skyrocketed to nearly $US750 a share and it has become one of the world's most highly valued companies. It has settled back in the past month and traded at $US693.08 on Wednesday on Nasdaq.

Page and Brin were co-ranked at No. 5 this year in Forbes' 400 list of U.S. billionaires. Each is estimated to have a net worth of $US18.5 billion ($21 billion).

In May, Brin married his longtime girlfriend, Anne Wojcicki, on a sandbar in the Bahamas.

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