Acclaimed mockumentary filmmaker Christopher Guest is joining the cast of the "Night at the Museum" sequel says The Hollywood Reporter.

The "Spinal Tap" actor will play Ivan the Terrible in the comedy adventure, joining Ben Stiller, Robin Williams, Ricky Gervais and Owen Wilson.

Jon Bernthal (Al Capone), Bill Hader (Gen. George Armstrong Custer) and French actor Alain Chabat (Napoleon) were also recently cast.

Even 'Museum' scribes Robert Ben Garant and Thomas Lennon will make a cameo as the Wright brothers. The film is currently shooting in Vancouver.