Meghan Markle Has 'Tamed' Prince Harry's Bad Habits

Prince Harry is a changed man inside and out thanks to his fiancee, Meghan Markle -- going from full-fledged bachelor life to living on a leash ... lovingly, of course.

We spoke with royal expert Katie Nicholl -- who's familiar with Harry's inner circle -- and she tells us Harry has kicked a lot of his old bad habits since getting with Meghan. We're not just talking food and lifestyle here -- though, that's part of it. It's more big picture.

Nicholl says Harry, for instance, will pass on tequila shots at a wedding now -- and even make excuses to call it an early night. He's also doing yoga with Meghan too, and eats clean with her. In other words ... Meghan's L.A. lifestyle is alive and kicking in London.

As Katie puts it ... Meghan has certainly "tamed" Harry. Nicholl spills even more tea in her new book, "Harry: Life, Loss, and Love."