The Harry Potter author was seen cheering on the contestants at the Blackpool Tower Ballroom, especially Susan Calman and her professional partner Kevin Clifton.
JK took to Twitter to show her support for Susan shortly before the show began on BBC One, posting a picture of a present she took to the seaside for her friend before she danced.
She shared a picture of a cupcake with purple icing and three paddles with "10" on them.
Earlier in the day, JK teased that she was in the city, posting a photo of the Big Wheel on Blackpool pier to her Twitter account.
She played coy when it came to revealing why she was visiting the city just hours before showtime, simply captioning the photo, "excited".
But it's not just JK who was excited about her time at Strictly.
A number of viewers were equally happy after they spotted her in the audience cheering on the quiz show host - and they didn't exactly hide their excitement:
Though others were left a little confused by her blink and you'll miss it appearance:
Is that @jk_rowling I see on strictly ]]>😂💛