Donald Trump reportedly didn't know India and China shared a border

Did you already know that India and China share a border?

Congratulations. You're better at geography than the President of the United States of America.

Donald Trump once left Indian prime minister Narendra Modi shocked after telling him India and China didn't share a border, according to a new book by two Pulitzer-winning journalists, news.com.au reports.

In the book, A Very Stable Genius, Washington Post journalists Phillip Rucker and Carol Leonning claim the incident took place during a face-to-face meeting between the pair, although it doesn't specify which one.

"It's not like you've got China on your border," Trump told Mr Modi. The Indian leader's eyes "bulged out in surprise", according to one of the President's aides.

Modi's expression "gradually shifted, from shock and concern to resignation" following Trump's remarks.

The aide said they felt Modi probably "left that meeting and said, 'This is not a serious man. I cannot count on this man as a partner'."

India "took a step back" in its diplomatic ties with Washington after that meeting. They are due for talks later this year, with Trump potentially visiting the country in February.

If confirmed, this would mark Trump's first visit to India since he was voted to power in 2016.

This isn't the first time Trump's geographical knowledge has been called into question.

According to a TIME magazine correspondent, he had to be corrected at a briefing where he falsely claimed Nepal and Bhutan were in India.

He also reportedly "mispronounced Nepal as 'nipple' and laughingly referred to Bhutan as 'button'."