Star's boyfriend John Mayer writes her a special song

Friends actress Jennifer Aniston celebrates her 40th birthday today.

And the star’s on-off boyfriend John Mayer, 31, has penned a track to mark the milestone.

‘He did write a special song just for her for her birthday,’ a source tells People. ‘No word yet on his performance!’

It’s rumoured the musician plans to propose, after he hinted on his blog that he’d bought an engagement ring.

Jennifer threw an early birthday party at her Beverly Hills home on 7 February.

Among guests invited to the bash were Sheryl Crow, 46, and Courteney Cox, 44.

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