The Ministry of Defence has denied a Hawk fighter jet flew from Anglesey especially to take Prince William home.
The prince is beginning his military career in 2006
William, who had been on work experience with RAF mountain rescue in Snowdonia, was flown the 250 miles to RAF Lyneham on Wednesday.
Fending off criticism over the cost, the MoD said the jet was on a routine training flight and a seat was spare.
They also said the "familiarisation" with RAF planes was part of the prince's work experience.
William, 23, was flown from Anglesey by military jet to the RAF base in Wiltshire which is close to Prince Charles' Highgrove estate in Gloucestershire.
There had been some criticism that the flight had cost £20,000 just to give the prince a lift home. An MOD spokesman denied this.
"There was a spare seat, so we took him. It was entirely routine, we can do that - the flight was going anyway," he said.
The MoD said William simply filled a spare seat on board the Hawk
"It was a training flight for a pilot and they do routinely land at different airports so there was no extra cost involved."
William had been training with a mountain rescue team in Snowdonia this week, part of a programme which has also seen him spend in City institutions and learn about land management on a country estate.
A spokesperson for Clarence House said the prince was required to be back at his father's home on Wednesday because he was due to take part in an induction at Sandhurst to pick up his kit and boots.
The RAF, he said, had "very kindly agreed" to give him a lift down as they were flying anyway.
"Like every cadet, Prince William is required to undertake military preparatory work prior to his entry to Sandhurst next year," he added.
"William's work experience programme is based on key aspects of the RAF's training for the mountain rescue team.
"Familiarisation with its air craft forms part of that programme."