Jessica Simpson is trying to warn Jennifer Aniston to be careful with new man John Mayer, because he is a notorious “ladies man”.

The wannabe country singer, who is currently dating American football star Tony Romo, was said to be jealous that her ex-boyfriend Mayer is dating the Friends star, but sources claim the green-eyed monster people are seeing is actually just concern.

A source says via Transworld News: “Jessica wants Jen to be aware of what she’s letting herself get into with John. She doesn’t want her to make the same mistakes. John is a ladies man.”
 
Others are also letting the rocker’s true colours be known, with a friend of Mayer adding: “He’ll spend every waking minute talking to someone and spending time with them and then move on to the next girl,” said the friend.

Is Jennifer making a mistake with John like she has done with all of these men?