The lady in question is leggy Kimberly Guilfoyle, last linked romantically to former White House communications director Anthony Scaramucci in October - ironically after his nine months pregnant wife filed for divorce from him.
"Don Jr. and Kimberly are seeing each other, and are having a great time", a source said.
The two were spotted on Sunday evening at a party for the newly confirmed Ambassador to Germany, Richard Grenell.
Guilfoyle is a former attorney and co-hosts The Five on Fox News.
"On The Five, Guilfoyle is part of a roundtable ensemble of FNC personalities who discuss, debate and even debunk the hot news stories, controversies and issues of the day", her bio reads.
The divorce is reportedly "uncontested", but now he's trying to find out how much money she has. They separated in 2009, then legally divorced.
Reps for Trump Jr. and Guilfoyle did not respond to Page Six's request for comment.
Guilfoye married Gavin Newsom in 2001.