Without any doubt the most known royals are those of the United Kingdom and then, because of the enormous Spanish-speaking community, the Spanish royal family.
Diana died in 1997. People who were younger than 8 or 9 years when the dreadful accident happened are now 25, 26 years old. My guess is that this younger generation will know who Catherine is and have little memories about her late-mother-in-law who died 17 years ago. It is sad, history is fast, very fast. I mean: how many people will still know who the late Princess Margaret was? Soon Princess Margaret will just become a footnote in a familial history.