Lewis Hamilton and Nicole Scherzinger
10/21/2011 at 04:00 PM EDT
Their relationship apparently didn't have that X Factor
Nicole Scherzinger, a judge on the music competition show of the same name, has split from her boyfriend of four years, race-car driver Lewis Hamilton.
"They'd been long distance for a long time and it's just been hard," a source close to the couple tells PEOPLE.
"They both tried to make it work, but their careers kept them apart. So for now it's over. They think this is what's best. They're definitely going to stay friends."
Packed schedules, including Scherzinger's duties on The X Factor
and Hamilton's position as a leading driver for Formula 1, have kept them both increasingly busy.
Scherzinger, 33, is based in Los Angeles, while Hamilton, 26, regularly travels the world and has a house in Switzerland.
It was just last July when the couple were the subject of widespread
, though she quickly denied they had plans to marry.
The pair first met at the European Music Awards in Munich, Germany in November 2007.