Monday's episode of The Voice featured a celebrity guest appearance by Big Bang Theory star Kaley Cuoco who came to support her sister, aspiring singer Briana Cuoco.

Briana, who works as Kaley's personal assistant, was shown with her sister and parents before taking the stage. Her rendition of Lady Gaga's You & I led Christina Aguilera and Cee Lo Green to turn their chairs around to show their interest in coaching her.

"She kept my attention, which is important in the blind [auditions]," said Aguilera.

When the coaches turned their chairs around, Kaley cried and her parents jumped up and down for joy as host Carson Daly stood beside them. In the end, Briana chose to join Aguilera's team.

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Another standout of the night was 15-year-old Timyra-Joi. The teen blew all four judges away when she sung Alicia Keys' Girl On Fire. After she performed she told the judges why she was getting started on her singing career at such a young age.

"I'm looking to find who I am as an artist," said the teen. "When I get on stage, hopefully this will be just the beginning."

She also chose to join Aguilera's team.

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Aguilera and Green are returning to The Voice after a one season hiatus where they focused on their music careers. They were replaced by Shakira and Usher for season 4. Shakira and Usher will return to The Voice for season 6 when it premieres in spring 2014.

The Voice's week 2 of competition continues Tuesday, Oct. 1, at 8 p.m. EST.

Watch Briana Cuoco's performance of You & I.

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The Voice Season 5, Kaley Cuoco, Christina Aguilera, Cee Lo Green, The Voice