Its not the first time that he's made the claim but Trump is reported to have stated, in front of a group of senior Republicans and Democrats, that he let the popular vote because of 3 to 5 million illegal votes. This claim is entirely in character in that the facts don't matter to Trump, what matters is what he believes or, more accurately, what he needs to believe to support his view of himself.
Trump's language is peppered with superlatives where what he is going to do will be 'a beautiful thing' or 'a wonderful success'. He uses the same terms in relation to the people he chooses to work with where they are always 'wonderful people'. It seems that he cannot bear being associated with anything that isn't 'the best' or 'wonderful' or 'excellent' and by the same token, he cannot bear being associated with anything where he doesn't come first. So, Hilary didn't win the popular vote because of the illegal votes and his inaugural crowd was the biggest in history irrespective of any evidence to the contrary.
And, on the subject of the inaugural crowd, relating the various crowd photos to Google Maps image of the National Mall, gives another indication of the relationship between Trump's crowd and the crowd that attended Obama's inauguration in 2009. But this probably qualifies as an 'alternative fact'.
