Katy Perry has entered her "zero f****" 40s.

The 'Teenage Dream' hitmaker - who has four-year-old daughter Daisy with fiance Orlando Bloom - celebrated her milestone birthday last month and admitted that with getting older, she's learned to care less about what other people think.

She told The Sun newspaper: "I guess I did step into what I call a 'zero f**** 40'.

"A therapist told me one day, 'No one can make you feel something about yourself that you already don't feel about yourself'.

"So if someone says something about me that isn't true, it doesn't affect me because I know who I am now. I know myself better than ever.

"I care a lot about the things that are worth caring about but if someone's not being kind or saying untrue things, then it doesn't really matter."

Despite her and Orlando's huge success, Katy insisted they still lead "normal" lives and she has no desire to slow down her career.

She said: "We are so privileged to live such big lives that we've created.

"But we do have very kind of normal lives as well.

"We have all the bits and bobs in between. But we never take it for granted. Every day is a blessing.

"I'm working as hard as I've ever worked and I continue to.

"I never put any terms, conditions or limits on my dreams. I suggest that no one else does either because you might surprise yourself how much you can achieve when you believe."

The 'Woman's World' singer has just announced she will be touring the UK next year and after Prince Harry and his wife Meghan, Duchess of Sussex, were spotted in the audience at the final show of her Las Vegas residency in November last year, Katy admitted she'd love to see the royal's estranged brother, Prince William, and his wife Catherine, Princess of Wales, at one of her British gigs.

She said: "Oh, they're totally invited. I love them so much and I am so proud of Kate.

"She is amazing. She is beautiful inside and out."