The 36-year-old singer, who has had an on-off relationship with Mr Musk since 2018, apparently only learned via social media that he had taken X Æ A-12 - or X for short - to the briefing with Donald Trump on Tuesday.
X Æ A-12 also stood beside his billionaire father and Mr Trump as they spoke, at one point appearing to attempt to address the president as Mr Musk answered questions.
X is one of three children Mr Musk and Grimes share, alongside his younger siblings Exa Dark Sideræl and Techno Mechanicus, or Tau for short.
Read more:Elon Musk's X to pay Trump $10m compensationSky News' correspondents give views on Trump's call with Putin.
While photographers took pictures, Mr Trump said: "X are you ok?
