Christina Aguilera was never known as a sugary sweet pop star, even when she first debuted alongside other starlets Britney Spears, Jessica Simpson and Mandy Moore in the early 2000s. On Monday night's The Voice, some thought Christina Aguilera was decidedly icy towards superstar newcomer Justin Bieber.

Justin Bieber made a guest appearance on NBC's The Voice on the April 17 show to debut the video for his new single, Boyfriend.

Before making his exit, Bieber went to say goodbye to mentors Blake Shelton, Cee-Lo Green, Adam Levine and Christina Aguilera. When bidding au revoir, Bieber shook hands with the male mentors and smiled. When he reached Ms. Aguilera, who put out her hand for a handshake, he gave her a peck on the cheek instead. Rather than looking starry-eyed, Christina Aguilera was caught giving him an icy stare.

Twitter blew up with users commenting on the chilly goodbye between Bieber and Aguilera.

Famously pleasant human being Christina Aguilera's expression post-hugging Justin Bieber has made my day, posted Twitter user John Lucas.

And that was Christina Aguilera overtly hating on Justin Bieber. #TheVoice tweeted user Kerri Mason.

Flipped to The Voice for a second & Justin Beiber was on. It sure seemed like Christina Aguilera despises him. + bonus points to Bieber LOL, wrote user Chuck Jacobson.

Christina Aguilera was so rude to Justin Bieber on #TheVoice last night! Watch her give him the cold shoulder, tweeted Hollywood Life.

Hollywood Life caught up with The Voice mentor after the show, where she reportedly didn't seem all that impressed with him [Justin Bieber].

You know, he's definitely popular with the ladies and he came on the show tonight and it was a fun burst of energy, Christina told exclusively after the show. He is really a charismatic guy and cute.

Aguilera's response to Bieber might have stemmed from something completely unrelated to the young heartthrob.

Earlier that night, Christina Aguilera had to let go one of her favorite contestants, Ashley De La Rosa. Maybe my saddest day of #TheVoice to date- letting @UKnowAshleyDLR go was extremely hard. She is a star who we have NOT seen the last of!! Aguilera tweeted to fans on Tuesday.

Maybe when Justin Bieber returns to The Voice on May 8 for the finale he and Aguilera will share a more loving moment.

Do you think Christina Aguilera dissed Justin Bieber? Watch the video below.