Lord, he must be a monster. This woman was married to Russell Brand, and never was there such a public outcry. 

In case you require a recap, Mr. Mayer has previously dated Jennifer Aniston, 43, Cameron Diaz, 39, Jennifer Love Hewitt, 32, Kim Kardashian, 31, and Taylor Swift, 22, amongst others.

A source says most of Katy's inner circle, as well as ex-husband Brand, are worried about her choice of partner. Yikes.

An insider told the Daily Star: "John has a big reputation as a serial womaniser. If people thought her ex, Russell Brand, was bad, John is notoriously a lot worse. Katy's friends are worried this is just a rebound bit of fun but will end with her getting really hurt."

John - who also dated Jessica Simpson, 32, in between her relationships with Nick Lachey and Eric Johnson - famously described his time with Jessica as similar to horsing into a load of drugs.

He said: "That girl is like crack cocaine to me. Sexually it was crazy. That's all I'll say." And yet he continued: "It was like napalm, sexual napalm. Did you ever say: 'I want to quit my life and just f**king snort you?'

That sentiment just gets more beautiful with age, John. No wonder you're such a revered lyricist.

>Katy Perry dated Mayer before Brand