The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

The King must have an HEIR
Game of Thrones Season 6, Episode 7

I'm your son, your only living HEIR.
Game of Thrones Season 2, Episode 2

You do see that? He gets
you back as his HEIR.
Game of Thrones Season 4, Episode 7

He is the rightful HEIR.
Nothing can change that.
Game of Thrones Season 1, Episode 7

- She's the rightful HEIR.
- Why?
Game of Thrones Season 5, Episode 6