The remark came during a G7 meeting in closed-door discussions between heads of state. The Wall Street Journal, which broke the story, cited a senior EU official.

25 million people represents a fifth of the Mexican population, and about two and a half times the estimated number of undocumented immigrants in the United States.

The Wall Street Journal – Behind the Scenes at G-7 Meetings, Allies Dismayed by Trump’s Jabs
Pew Research Center – 5 facts about illegal immigration in the U.S.