Ariana Grande (Getty Images)

Ariana Grande posted an emotional apology on Twitter after an apparent terrorist attack killed 20 of her fans at a concert on Monday.

 

Grande was reportedly in "hysterics" after the attack, according to TMZ. "She's in no condition to perform," a source told TMZ.

 

It was expected that Grande's next scheduled concert on Thursday night in London will be canceled, along with upcoming shows in France, Poland, Switzerland and Belgium.

 

The singer had reportedly just finished her Monday night concert with a performance of "Dangerous Woman" and exited the stage when a nail bomb detonated in a crowd of her fans.