By David Owen at The Hilton in Buenos Aires

Princess Hisako of Takamado arrived in Buenos Aires last nightSeptember 6 - At the International Olympic Committee (IOC) gathering in Lausanne in early July, Madrid 2020 injected momentum into its once flagging campaign by unleashing its royal rock star.

Felipe de Borbón y Grecia, Prince of Asturias, took to the stage with a winning mix of humility and regal bearing and brought the house down, leading even one of the less impressionable IOC members to describe him as "the star performer of the day".

Now it is Tokyo's turn.

Earlier this week, an elegant and approachable Japanese woman with perfect English vowels glided discreetly into the lobby of Buenos Aires Hilton, greeted old friends and talked with knowledge, vivacity and passion about a range of sports, from football to fencing.

This was Princess Hisako of Takamado, and tomorrow morning, at some point between 10.30 and 11.15 local time, she is expected to address a far more distinguished audience: the more than 100 IOC members who collectively will decide whether the Japanese capital, Istanbul or Madrid will host the 2020 Olympic and Paralympic Games.

According to the Imperial Household Agency, the Princess is to voice her appreciation for the IOC's support with post earthquake/tsunami reconstruction.

Based on yesterday's appearance, she could also provide a big boost for the bid in private meetings with IOC members over the next two days, if it is deemed appropriate to deploy her in this way.

Princess Akiko of Mikasa is also expected to arrive in Buenos Aires to support Tokyo 2020 ahead of the vote on Saturday Princess Akiko of Mikasa is also expected to arrive in Buenos Aires to support Tokyo 2020 ahead of the vote on Saturday

With the Tokyo bid having been knocked badly off balance by growing concerns about the toxic legacy of the Fukushima nuclear accident, the arrival on the scene of such an articulate and charming advocate of sport and Japan looks perfectly timed from the Tokyo perspective.

In this tight and astonishingly volatile race, the Princess' presence is the sort of new ingredient that could make a real difference with this singular electorate, many of whom hold royalty in the highest esteem.

Another imperial family member, Princess Akiko of Mikasa, is also expected to be present for the final hours of the campaign.

The all-important vote is scheduled for 3.45pm-4.00pm, local time.

Announcement of the winner should come just before 5.30pm.

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