Princes William and Harry missed part of their charity motorcycle ride after they were struck down by upset stomachs.

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The royals began their 1,000-mile ride across South Africa on Saturday (18.10.08) but less than three days into the journey, while riding in the Transkei region, they began to feel unwell.

Several other riders taking part in the Enduro Challenge were also hit by the bug, which saw the princes fail to complete a full day’s riding on Monday (20.10.08).

A source told The Sun: “This is a nightmare for any rider. Not only do they have to cope with a very bumpy ride – but the outfits take a lot of effort to remove.

“They couldn’t risk having an accident and have had to take it very easy indeed.”

The pair have since made it to the half-way point of the trek, Morgan’s Bay, and are said to determined to reach the finish line in Port Elizabeth by Saturday (25.10.08).

The princes – who are raising money for several charities including the Sentebale fund, which Harry founded to help children with HIV in Lesotho – are riding in a team of 10, including a police bodyguard and Harry’s girlfriend Chelsy Davy’s brother Shaun.