The `Promise This` singer - who is believed to have fallen out with the music mogul when he fired her from the US `X Factor` earlier this year - hired a plane trailing a cheeky message over the property he is currently renting in South Beach, Miami, to celebrate Simon`s 52nd birthday.

It read: "Simon Cowell is 52 today! Ha ha ha! Love Cheryl xoxo"

Simon - who famously axed Cheryl from the panel of the talent series after just four auditions - was said to have found the stunt "hilarious".

A source told the Sunday Mirror newspaper: "Cheryl knows he likes to keep his birthday quiet so he thought it was very funny that she was teasing him over it. They had a strong friendship outside of work.

"The past couple of weeks they have been back in touch and there`s no doubt they missed each other`s friendship."

"Cheryl`s been totally reborn in the past few months. That`s why she doesn`t care about poking fun at Simon. And she always used to worry about what he`d think and say all the time but she has a sense of freedom now."

However, Cheryl didn`t leave Simon`s birthday embarrassment there, declaring his age to her almost 600,000 followers on twitter.

Referring to the `X Factor` categories, she joked: "Simon Cowell is `52` Today... He is officially in the overs category .. Hehehehehe.. (sic)"

This isn`t the first time Cheryl has pulled a birthday stunt on Simon, as last year she sent the star three singing dwarves - who were decked out with a violin, drum and an accordion - wearing grey T-shirts and jeans to copy the TV mogul`s sense of style.

Simon was so thrilled by the gesture, he invited the group, actor Phil Holden and friends Ray Griffiths and Darren Horan to spend the day with him.

Phil said: "Simon saw us and asked, `Are you for me?` before bursting out laughing. He thought it was the best present he`d ever had. Cheryl said she thought it would funny for us to annoy him."
sections: Celebrities