SIR Andy Murray has lived up to his moody persona with a hilarious tweet to celebrate his 31st birthday.

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The tennis ace took to Instagram to share his birthday gift, a delightful hat in the shape of a cake featuring the words "happy birthday" and a candle on top, of course.

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I love birthdays.

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Looking rather glum, the gold medallist captioned the snap "I love birthdays" and prompted a massive response from fans.

Among them, his biggest fan, proud mum Judy Murray shared the picture to her Twitter page and captioned it with a laughing emoji.

It's not the first time the dad-of-two has joked about the perception of his attitude.

Late last year he took to social media with a photo of him in a Christmas jumper, again looking equally as glum.

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He joked about how much he "loved" his look.