The disco song, a staple of karaoke and sports events, has risen to a new level of prominence since Trump adopted it for campaign rallies in the United States before his presidential election victory last month.
Sportsmen have started mimicking a dance performed by the President-elect during the song.
YMCA shot up the Billboard dance/electronic sales chart as polling day approached on November 5, and finally hit No 1 after Trump’s victory the week of November 17.
Some musicians have distanced themselves from Trump’s use of their material, and Willis too initially asked him to stop using YMCA because it had become a “nuisance”.
But he added the Republican had obtained a political use licence for the song from BMI, which manages music performance rights, meaning it could be used freely.
And when the money started rolling in, BMI was told not to try to remove Trump’s use of the song.
“The financial benefits have been great,” said Willis.
“YMCA is estimated to gross several million dollars since the President-elect’s continued use of the song. Therefore, I’m glad I allowed the President-elect’s continued use of YMCA. And I thank him for choosing to use my song.
“For example, YMCA was stuck at #2 on the Billboard chart prior to the President-elect’s use. However, the song finally made it to #1 on a Billboard chart after over 45 years (and held on to #1 for two weeks) due to the President-elect’s use.”