Forgotten book about a witch

[NooNakedJacuzziness]

Need some help finding the title of a children's book I read (must be about 40 years ago now, so good luck!). It had a woman in it who was very beautiful but was a witch underneath. When she got angry green smoke came out of her nose.

Her pet/familiar was called Beezlebub. When she was eventually discovered to be a witch she was revealed to be hideously ugly and her outer disguise fell away. Anyone recognise it? I've Googled but no luck, been thinking of it for years!

The Wickest Witch in the World, Beverly Nichols.
I don't know why but it stuck in my head since childhood too

THANK YOU @CoffeeSlice, that's it! I really needed the author's name. I thought it was called something like The Worst Witch or The Wicked Witch but there are tons of books with similar titles. I've just googled it and remember the pony called Snowdrop and the little girl.

Thanks again - hoping it's still in print.

I read it as a child too but didn't keep it. Found a copy on one of the second hand book sites a few years ago. Re-read it as an adult and it's still a good story. Good luck finding a copy

There's a hardback on EBay for £207 - not sure I can justify that but I'll keep looking! Thanks again @CoffeeSlice, so pleased you knew the author

Saw this on Amazon

Thanks - much better price