Prince William Spends 26th Birthday with Girlfriend

By Simon Perry

06/22/2008 at 05:25 PM EDT

Add one more photographer to those snapping away at Prince William – his girlfriend.

Amateur shutterbug Kate Middleton got a close-up of William when they goofed around at a polo match on his birthday Saturday.

The royal lovebirds were under a gazebo on the drizzly mid-summer's day in Gloucestershire, England, when Middleton, 26, took out her camera. She shot away, gleefully showing both William – who turned 26 – and his group of pals the images on her digital camera.

"She was happy to show her pictures to everyone," says a witness.

The prince and Middleton, who have been dating for about six years, have been spending a lot of time together before he heads away for several weeks. William will soon take to the seas to conduct a tour in the Caribbean for the Royal Navy.

Earlier this month, he and Prince Harry, 23, took their girlfriends on a double date to a charity boxing match, and last Monday Middleton was seen laughing alongside Harry as they watched William parade through Windsor Castle's grounds in spectacular ostrich-plumed hat and flowing robes on the day he was made a knight.