The Twilight couple parted ways for good earlier this year (13) after briefly giving its relationship another try following Stewart's "momentary indiscretion" with her married Snow White and the Huntsman director Rupert Sanders.
The British hunk sparked speculation of a new romance after he was photographed driving in Los Angeles on Sunday (30Jun13) with a woman purported to be Keough - but now a spokesperson for Stewart's former Runaways co-star has shut down the claims.
Her rep tells JustJared.com, "Riley isn't dating Rob. And I can confirm that Riley was not photographed at all this weekend."
Keough, the actress daughter of Lisa Marie Presley, was last said to be engaged to Magic Mike star Alex Pettyfer, although reports suggest the couple also split in early 2013.