Julianne Hough wowed fans as Sandy in Fox’s live musical production Grease: Live! on Sunday evening–but probably none more than brother Derek Hough, who gave his Dancing With the Stars costar a big shout-out.

“Killin it ! #GREASELIVE my Sister ! Proud as a mutha,” the Dancing With the Stars pro captioned this short clip of sister Julianne Hough and Aaron Tveit. You can hear the cheering in the background as Hough and his friends watch the production.

A video posted by Derek Hough (@derekhough) on Jan 31, 2016 at 7:19pm PST

A short time later, Derek shared even more of his pride in his sister.

“Singing live for all to hear!!!! Nailed it! #emotional #proudbigbrother,” he captioned yet another clip of Julianne Hough. Listen for Derek’s accolades directed at his sister in the background.

A video posted by Derek Hough (@derekhough) on Jan 31, 2016 at 9:08pm PST

Julianne Hough was like a kid at Christmas ahead of Sunday’s performance.

The transformation has begun!!! #GreaseLIVE #TONIGHT on FOX https://t.co/oxK2193BLB

— Julianne Hough (@juliannehough) January 31, 2016

It's finally here!! @GoGrease is on NOW! #GreaseLive ❤️ pic.twitter.com/ZAehQHOb5I

— Julianne Hough (@juliannehough) February 1, 2016

Did you see Julianne Hough–along with Aaron Tveit, Vanessa Hudgens, Keke Palmer, Carly Rae Jepsen, and more in Grease: Live! on Sunday night?

Julianne Hough just NAILED "Hopelessly Devoted to You" on #GreaseLive! Give it your grade: https://t.co/4XrSYyGu2S pic.twitter.com/NVnP1AWfa9

— TVLine.com (@TVLine) February 1, 2016

Is it any wonder Derek Hough is so incredibly proud of his little sister?