Laura Carmichael has revealed George Clooney was "so brilliant" when he shot a Downton Abbey cameo.

The Hollywood heartthrob agreed to appear in a special episode of the hit period drama for British charity Text Santa. While fans will have to wait until Christmas to find out more about his character, Laura, who plays Lady Edith Crawley, was lucky enough to see all the goods on the day of filming.

"It was amazing; we didn't really know if it would happen until he turned up. We were filming away and then we heard he had arrived and we were like, 'No, has he really?'" she revealed on British TV show This Morning.

"He was wonderful, he was so brilliant. There's a very brilliant moment with [Dame] Maggie [Smith] and George. Maggie does a very comedy move, George goes to kiss and Maggie ends up on the floor. It was wonderful, she was hilarious."

The cast were also able to see the funny side of a recent gaffe, involving a modern-day water bottle appearing in the background of a still of Laura and co-star Hugh Bonneville in the period drama. The incriminating object was clear to see on the mantelpiece and the image circulated around the world.

"It looks like it's mine doesn't it? That's the terrible thing," the 28-year-old sighed. "We do these stills as we're shooting and if you turn the camera just slightly to the left or right you'll see the piles of bottles, crew members and wires that are modern day, so for us one bottle is quite easy to miss, which is what happened. We found it hilarious that people couldn't get their heads round it."