Brandywine Realty Trust has plans to demolish an existing office building off First Avenue in King of Prussia to make way for a new 100,0000-square-foot office building. A three-story, 54,338-square-foot office building at 650 Park Ave. now stands on the property. Brandywine has received approval from Upper Merion to develop the four-story 100,000-square-foot building in its place. It was designed by Coscia Moos Architecture. Through a spokeswoman, Brandywine declined to comment on the project. The timing of its development couldn't be determined.