(CNN) Canada's Governor General helped Britain's Queen Elizabeth down some stairs and ended up raising eyebrows, after touching the monarch's elbow, in defiance of royal protocol.

David Johnston -- the Queen's representative in Canada -- said he was concerned about the monarch "stumbling" during a visit to Canada House in London on Wednesday.

In a clip filmed outside the building, which houses the Canadian High Commission, Johnston can be seen touching the Queen's arm as she walks down a set of steps.

"I'm certainly conscious of the protocol," David Johnston told CNN partner CBC News following the visit to celebrate the 150th anniversary of Canadian Confederation. "I was just anxious to be sure there was no stumbling on the steps."

"It's a little bit awkward, that descent from Canada House to Trafalgar Square, and there was carpet that was a little slippy, and so I thought perhaps it was appropriate to breach protocol just to be sure that there was no stumble," he explained.

Read More