Trump once questioned Richard Branson's billionaire status

Richard Branson's new book 'Finding My Virginity' reportedly includes a 2004 letter where Donald Trump questions the Virgin Group founder's billionaire net worth status.

According to the Independent, which reprinted excerpts of the letter from the book, Trump was commenting on the difficulties faced by the airline industry at the time when he wrote to Branson.

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He said: "It is obviously a terrible business and I can't imagine, with fuel prices etc. that you can be doing any better in it than anyone else... actually, wonder out loud how you can be anywhere close to a billionaire and be in that business.

"Perhaps the title of your show, The Rebel Billionaire, is misleading?"

He was referring to Branson's Apprentice-like TV show which Trump also slammed for its dismal ratings.

The now-President then warned Branson: "In any event, do not use me to promote your rapidly sinking show - you are a big boy, try doing it yourself!"