A beaming Kate Middleton looked on as Britain's Prince William became a pilot of the Royal Air Force (RAF) as part of his current military career.

Middleton's re-emergence on the public stage immediately sparked fresh speculation that William, who will be 26 in June, could soon pop the question to his long-term girlfriend.

"It is certainly a very firm confirmation that they are back together again," said the BBC's royal correspondent, Nicholas Witchell.

The pair, who have known each other since university, broke up briefly a year ago and have since had an on-off relationship.

They recently went on a skiing holiday in Switzerland but Friday was the first time Kate took part in an official function at the side of the prince.

She was also present when William, a serving officer in the Household Cavalry regiment of the Blues and Royals, graduated from Sandhurst Military Academy in December, 2006.

William, now Flying Officer Wales, received his RAF pilot's wings from his father, Prince Charles, at a ceremony at Cranwell air force base in Lincolnshire, eastern England.

Charles' wife, the Duchess of Cornwall, and the sister of the late Princess Diana, Sarah McCorquodale, were among those present at the ceremony.

Following his four-month training, during which he learnt to fly fixed wing aircraft and helicopters, William is due to undertake a similar attachment to the Royal Navy.

DPA