Singer Britney Spears and rapper Iggy Azalea starred as best friends in their duet “Pretty Girls,” but the pair reportedly are far from best friends in real life. The song did not do well on the charts and Azalea has publicly blamed Spears.

"It's difficult to send a song up the charts without additional promo and tv performances etc. unfortunately im just featured," Azalea wrote on Twitter, clearly ducking from any responsibility for the song's failure. Azalea's comment was in response to one of her fans during a Twitter Q&A session Sunday night. The fan asked Azalea why the single had “flopped a little bit.”

Spears' fans did not like Azalea's answer and told her that Spears promoted “Pretty Girls” at an acceptable level. So Azalea burst out at the critical fan, saying, “My comment is factual, it applies to any song."

However, Spears did not remain quiet after Azalea's nasty comments on Twitter. She seemed to make a veiled reference to Azalea’s recently canceled “Great Escape” tour. "Can't wait to get back to Vegas. So thankful I have shows for the rest of the year to look forward to ... #YouWantAPieceOfMe," Spears wrote on Twitter. Though the songstress did not name Azalea in her tweet, her comments can be easily interpreted as an answer to Azalea.

Spears was the highest-earning female musician of 2012, when she took home $58 million. Since 2013, Spears has been doing a residency at the Planet Hollywood Resort and Casino in Las Vegas for two years and reportedly earns $15 million annually. The “Hit Me Baby One More Time” singer is booked until Dec. 31.

According to Billboard, Azalea had to cancel this year's “Great Escape” tour because it was “only 20 percent sold.” However, the rapper told her fans that she canceled the tour because she underwent “a different creative change of heart” and felt she deserved “a break.” The “Fancy” rapper is now looking forward to getting married to her boyfriend Nick Young.