The former Pussycat Dolls singer and the British Formula One champion, who went public with their romance in 2007, have parted ways once again due to their clashing schedules.
A source tells Britain's The Sun, "It's so hard to keep up a relationship when they're barely in the same country as each other.
"Both have supported each other in their careers and will continue to do so. But the nature of their work ultimately cost their relationship."
The report comes just weeks after Hamilton suggested he may be ready to propose to the singer, hinting, "We've been together for five years, which is quite a milestone really. But hopefully in the near future. Maybe before we get to six years."
The couple previously split in 2011, but later rekindled the romance.