The former Pussycat Doll has apparently ended her relationship with Grigor, who is 13 years her junior.
A source told The Sun: "Nicole is at a different stage in her life to Grigor. She really likes him but wants to settle down - something he's not quite ready for."
Former X Factor judge Nicole only went public with Bulgarian sports star Grigor earlier this year when they spotted kissing at a tennis tournament in Australia.
They were first romantically linked in November 2015, with sources saying they were "besotted" with each other.
Nicole's last previous relationship was with Formula One racing driver Lewis Hamilton. The couple split in January last year after a seven year romance.
Meanwhile, Grigor has previously been linked to Maria Sharapova.
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