The comparisons began as soon as Channing's relationship first made headlines.
They're both brunette, rock bobs and are in great shape, leading many in the Twittersphere to suggest the "21 Jump Street" star might have "a type."
Dewan finally chimed in on the comparisons after one of her followers brought it up again in the comments on her Instagram.
After posting a photo of herself on the red carpet at the Baby2Baby gala over the weekend in Los Angeles, one fan wrote: "FIRST OF ALL….whenever I hear of the 'striking resemblance' w/ Jessie J to Jenna Dewan ..my only thoughts are ummmmm no (sic)."
Following a joyful emoji, the comment continued, "Not even close. nd I don't have a horse in the race but gf you are untouchable (sic). Just trying to spread positive vibes, keep doing you…to an absolute outsider from a small town you are doing it seamlessly."
In the replies, Dewan kept it classy by writing, "positive vibes all the way," and adding a kiss emoji.
The response comes after Tatum made his first comments about the singer on social media earlier this week. Posting a photo from her concert at Royal Albert Hall, he added, "Whoever was there got to witness something special. Wow."
Channing and Jessie were first linked in October, while Dewan has been dating Tony winner Steve Kazee.