Fifth Harmony member Ally Brooke Hernandez hails from San Antonio.

The FOX show on Wednesday night checked in at official viewing parties located at the finalists' hometowns. Castro attended the Fifth Harmony party, located at Oak Hills Church where Hernandez sang in the choir, and appeared on TV cheering on the group.

Hernandez tweeted her thanks to Castro.

Castro was the keynote speaker at this year's Democratic National Convention. His speech drew comparisons to then-Sen. Barack ObamaBarack Hussein ObamaKrystal Ball tears into 'Never Trump' Republicans Sanders campaign announces it contacted over 1 million Iowa voters Iowa Steak Fry to draw record crowds for Democrats MORE's (D-Ill.) 2004 convention keynote speech.

Lis Smith, director of rapid response for Obama's 2012 campaign, tweeted that the "sky's the limit" for Castro after an appearance on "X-Factor."