From WENN.com

The unidentified man, thought to be in his 50s, was spotted carrying two knives near the monarch's home in the U.K. capital on Sunday afternoon (03Feb13).

He was subdued by police with a stun gun after allegedly acting aggressively when challenged. An investigation is ongoing.

Queen Elizabeth II and her husband, Prince Philip, were not in residence at the time of the incident, according to the Associated Press.