Nicole Scherzinger apparently broke up with Lewis Hamilton after a "furious" phone call about his reluctance to get engaged.
The pair started dating in 2008 but earlier this month it was reported they had called time on their relationship.
Shortly before the break-up was confirmed, Lewis gave an interview stating he was "hopeful" they would get engaged in the "near future".
Apparently his wishy-washy comment wasn't enough for 35-year-old Nicole, who was keen to settle down.
"Nicole was the one who had the courage to end it. She'd grown frustrated that Lewis wasn't keen to move forward and told him she wouldn't wait any longer," a source confided to British magazine Star.
"They ended up having a furious row on the phone about his half-hearted 'we might get engaged sometime in the next year' comments.
"Lewis told her that he was in no rush to get married. And for Nicole, this was the final straw. She told him that if he wasn't going to take things to the next level, then she would carry on without him."
Nicole is said to be "devastated", but sure that she made the right decision.
However 28-year-old Lewis apparently isn't dealing well with the split.
"He made the mistake of underestimating just how much Nicole wants to get married and become a mom," the insider sighed.
"Lewis was in total shock when she called time on him."
Nicole has been keeping busy with her role as a judge on The X Factor UK.
According to the source, she is keen to make up for "lost" time and find someone who will make all her dreams come true.
Lewis opened up about the break-up to Sky News earlier this week.
The Formula One star was beaten by Sebastian Vettel to the top spot in the German Grand Prix on Sunday and currently takes fourth place in the overall standings.
"I'm trying my hardest to be positive, but I'm going through a really, really tough time at the moment with the loss of someone really, really special in my life. My world's turned upside down," he admitted.
"But I have a job to motivate my team... So I'm really trying to pull myself together and keep my head up, but it's so hard to do."
© Cover Media