Aubrey O'Day's Song 'DJT' Was About an Affair, Was It Donald J. Trump Jr.?

If Aubrey O'Day had an affair with Donald Trump Jr. -- as some reports have claimed -- she barely tried to conceal it when she released a song ... about an affair, entitled "DJT."

The 2013 tune is about as on the nose as you can get ... featuring a phone convo between Aubrey and a guy, with her asking him, "You want to believe that everything with me was a lie? A fantasy?" He replies, "I'll always want you and always wonder about it, but it doesn't matter because I have to stay here."

According to the NY Post, Aubrey and Donald Jr. allegedly had an affair in 2011 -- while she was a cast member on 'Celebrity Apprentice' -- but eventually broke things off at the behest of Trump Sr.

The show aired in 2012, and Aubrey's song came out in 2013. At no point in the song does she explain the title, "DJT" ... but ya don't have to be a rocket scientist, especially when his full name is Donald John Trump Jr.

As we reported, Don. Jr.'s wife, Vanessa filed divorce papers last week, and our sources describe him as "relieved."

Aubrey's rep told us the singer would have no comment, at this time.