SweetPea:
Tutankhamun is not really important.
Who preceded and succeeded him are, though,
The predecessor was Ankheperure Neferneferuaten, one of the most controversial figures in Egyptology.
Some believe this king was, in fact, TWO kings with the same prenomen.
Others such as myself feel that this was Nefertiti - Tut's stepmother, acting first as her husband's co-regent, then as king in her own right for about two years.
Most of the statues in the "treasury", the second coffin and quartzite sarcophagus, and canopic coffinettes in Tut's tomb belonged to her burial...wherever that was.
Nicholas Reeves, an eminent Egyptologist, and leader in the field of the Amarna period, gave the following lecture about the mask in New York's Metropolitan Museum of art, and it is really worth a look.
http:www.youtube.com/watch?v=bxN1hm1TmJ0
What you saw in London WAS the real deal. I've benn hands on with it in 1980!
There are other Royal masks though...from the twenty first dynasty, especially that of Psusennes I, which are, IMO, more magnificent!