On November 17, 1998, museum trustees announced plans to expand the museum yet again. Museum personnel had been in discussion with Philip Johnson for some time regarding the need to alter Johnson's 1977 addition. Johnson's solution was to demolish both the 1964 and 1977 additions and create a new, much larger structure behind the 1961 building. Philip Johnson spearheaded the new design in collaboration with his partner Alan Ritchie. It would be one of the last projects on which Johnson worked. In August 1999 the museum was closed to the public for an extended period while the 1961 building was refurbished, the 1964 and 1977 additions were removed, and the new addition constructed.