If you think US President Donald Trump writes all his own tweets, it seems you'd be wrong.

We may have found out who is actually behind at least some of Mr Trump's posts on his favourite social media platform, after what seems to be a staff slip-up.

A tweet — complete with Mr Trump's signature #FakeNews and emulating his style of speech — was posted to his Twitter account at the same time his social media director Dan Scavino posted a duplicate tweet.

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Twitter users were quick to notice, with many pointing out Mr Scavino may have been using monitoring and posting tool TweetDeck, which allows users to post tweets to multiple accounts at the same time.

Mr Scavino has since deleted his tweet, but the version on Mr Trump's account remains posted.

Mr Scavino has previously insisted Mr Trump posts his own tweets, following media reports the President's tweets could be distinguished from his staff's because they used an iPhone, while he posted from a Samsung Galaxy.