If you study the below photograph carefully, you will see a thin old man with a short mustache sitting approx. 8 rows up - just over goalie Roger Vachon's head (and slightly to the left). This isn't the best picture but once your eyes get accustomed, you will be able to clearly point him out.
I have no idea how Adolf Hitler was able to attend this game without attracting notice but I guess when the whole world thinks you are dead, it's easier than you think to get around unnoticed.
Hitler would have been 82 years old at the time but by all accounts, he developed a fascination with professional ice hockey. Most likely because many of the players were of Scandinavian/Nordic descent and fit his description of what a "master race" would look like if you outfitted them with ice skates and curved sticks and gave them a puck to play with.
Hitler was especially enamored of Bobby Orr, who can be seen in this photo bearing down on the goal while teammate Johnny Bucyk looks on behind him - hoping for a rebound (and a cheap goal).
If you could zoom in on Hitler's face in this photo at this key moment of the game, you would see him pumping his fist with his mouth agape as his blonde-haired blue-eyed hero zeroed in on yet another goal for the home team.
I don't think Hitler lived long enough to see Orr and the Bruins win another Stanley Cup later that year so this might have been the last public sighting of the most evil man of the 20th Century (excepting perhaps Josef Stalin or Scott Baio).

Forget Hitler - Rogie’s wondering where defenseman Larry Hillman (3) and Bill Mikkelson disappeared on this play. Fred Stanfield (17) and Don Awrey are also seen in this photo.
Forget Hitler - Rogie’s wondering where defenseman Larry Hillman (3) and Bill Mikkelson disappeared on this play. Fred Stanfield (17) and Don Awrey are also seen in this photo.