"Just when I thought our day in Africa couldn't get any better.... We are engaged!!:):)" Arnold, 20, captioned a photo on Instagram Tuesday of herself and new fiance Sam Cusick smiling from ear to ear.
Cusick apparently proposed with a pear-shaped diamond ring featuring tiny diamonds on the band and around the large stone itself.
"My best friend in the whole entire world got engaged to the love of her life today!" Carson captioned the same photo Arnold had posted. "I am crying tears of joy, I could not be happier!! I love you guys, congrats!!!"
Arnold competed on the ninth season of So You Think You Can Dance in 2012 and made the Top 8 contestants. She then joined ABC's Dancing with the Stars, serving as a pro in Season 16 with celebrity partner Victor Ortiz and then dancing in the show's Troupe ever since.