Mayer 'pens birthday song for Aniston'

John Mayer has reportedly penned a special birthday song for Jennifer Aniston.

An insider told People that Mayer, who picked up two Grammys on Sunday, wrote the tune in honour of the former Friends star turning 40.

"He did write a special song just for her for her birthday," said the source.

Aniston celebrated reaching the milestone with an A-list bash at her Hollywood home on Saturday.

Earlier this week, she told Ellen DeGeneres that she feels good about turning 40, saying: "I feel better than I ever felt in my life."

However, she admitted that she "flipped" out after discovering a "really long grey hair".