33 is an important number to Freemasonry. I can't seem to get a clear picture of why. It could be nothing more than that Jesus was ostensibly crucified at 33 years of age. The masons seem to be pretty eclectic about where they get their symbols from.
In any case, here's some places I've found the number 33.
11/22/1963 - JFK assassinated
11+22 = 33
9/11/2001 - WTC attacks
9*11 = 99
2+0+0+1 = 3
99/3 = 33
Admittedly, these are "data-mining" but it's not torturous data-mining.
The Wikipedia article for the number 33 claims that 33 is somehow related to the Star of David but doesn't explain how. There are 13 points in the star, 24 edges and 12 triangles. Sums and differences of these yields 1, 11, 25, 36 and 37. I see no relation to 33. The only way I can squeeze 33 out of the star is to consider it as two triangles super-imposed - each with 3 points (or sides) yielding 3, 3. However, 3, 3 is not the same as the number 33. The highest degree of freemasonry is not 3, 3 it is 33. Argh.
Prince William's birthday is June 21st. In Britain, that would be written 21/6. 6x6x6 = 216