The 24-year-old singer and 33-year-old country star attended the 2017 Grammy Awards in Los Angeles, where Lovato was nominated for Best Pop Vocal Album for Confident and Underwood for Best Country Solo Performance for "Church Bells."
The singers both turned heads in dresses with keyhole necklines, with Lovato in a gold gown made sheer by the netted material and Underwood in a red lace dress with a thigh-high slit.
"This year he was like, 'You know, I feel like you've been holding back and you can open up to the world. So show your sexy side!'" she shared.
Lovato and Underwood lost to Adele and Maren Morris, respectively, in their nominated categories, but wowed with their performances at the awards show. Lovato led a tribute to the Bee Gees, while Underwood sang "The Fighter" with Keith Urban.
"It's #Grammy day!!" Lovato had tweeted earlier in the day. "Still can't believe I was nominated and now I get to perform tonight?!! Dreams come true people!"
Lovato released her album Confident in October 2015, which includes the singles "Cool for the Summer" and "Stone Cold." Underwood released Storyteller the same month, which features the singles "Heartbeat" and "Church Bells."