Why is Kate now known as Catherine?

[ShoppingDays]

Why is Kate now going to be known as Catherine? If she was Kate before then why should she have to change what she's known as?

I think it is because it is seen as more "fitting" for a potential princess. A bit like no one (afaik) calls the Queen "Lizzie" or Charles "Charlie"

To sound more formal and Royal and less "one of us". TBH, I thinkg Princess Katherine sounds bettern than Princes Kate.

And also I think her family always call her Catherine....

I read she was always Catherine, the press shortened it to Kate to fit better in headlines.

Not a fan of the royal family so when 1st daughter was born the day after the queens 80th birthday put my foot down at calling her Elizabeth, that's right we called her Kathryn.

Yes, she has always been called Catherine by friends and family, 'Kate' was a media-given nickname (as was 'Di' since Diana was always known as Diana or 'Duch')