The singer took to Instagram on Wednesday, November 27 and shared a photo of a black heart with the girl group's name written in pink and white.
"#PCDReunion," she wrote alongside the post.
Bandmates Kimberly Wyatt, Ashley Roberts and Jessica Sutta posted the same photo and caption.
The group will reunite for the final of U.K. TV singing contest "The X Factor: Celebrity" on Saturday, November 30.
The "Don't Cha" hitmakers split in 2010 but rumours of a reunion have swirled in recent weeks, and Nicole's fellow "The X Factor" judge, Louis Walsh, let the big news slip on British breakfast TV show "Lorraine" on Monday.
"The Pussycat Dolls are the guest! There's an exclusive for you," he excitedly told host Lorraine Kelly.