Security concerns have led Kate Middleton, Prince William's on-off girlfriend, to pull out of a Dover to Calais Chinese dragon boat race.
Prince William and Kate Middleton split up earlier this year
Organisers said the security concerns related to media coverage of the event.
Miss Middleton was due to be part of the all-female crew of the Sisterhood, racing against the Brotherhood, crewed by men on 25 August.
The Beauty v Brawn cross-Channel challenge was organised to raise money for children's charities.
A spokeswoman for the Sisterhood said: "Kate Middleton has withdrawn from the race due to security issues surrounding the recent media circus."
Media interest in the race had intensified after speculation Miss Middleton, 25, had resumed her relationship with the second-in-line to the throne.
Prince William and Miss Middleton split up earlier this year after a four-year relationship but are reported to have attended several events together during the summer.
World record attempt
Miss Middleton had been persuaded to join the challenge by Sisterhood member Alicia Fox-Pitt, a school friend from Marlborough College.
She was training to be at the helm of the boat for the race.
The race route covers more than 20 miles of open sea and passes through one of the world's busiest shipping lanes.
Both crews are attempting to break the world record for a dragon boat crossing, which currently stands at seven hours 45 minutes.
The women are set to become the first all-female team to cross the Channel in a dragon boat.
The race is in aid of the Babes in Arms charity, which sponsors research into abnormalities in newborn babies, and the children's hospice charity Chase.