Awkward ex run-in!

Lauren Conrad got spooked by a ghost of relationships past at Matthew Morrison's October 29 Halloween party: her ex-boyfriend, Kyle Howard.

Upon spotting the My Boys actor, 33, at the Bing/Svedka-sponsored bash at West Hollywood's Voyeur, Conrad -- who attended without new beau Derek Hough -- "got flustered," a source tells the new issue of Us Weekly. Dressed as Britney Spears, Conrad immediately retreated to the restroom to primp. Later, Howard "couldn't take his eyes off Lauren" as the former Hills star flirted with Chace Crawford.

For more on the exes' run-in, check out this week's Hot Stuff video, as explained by Us' Senior Editor Ian Drew and special guest Wale.

Also in the roundup: Connor Cruise tells Us dad Tom approves of his budding music career as DJ C-Squared, new details on Lady Gaga's romance with Vampire Diaries star Taylor Kinney, and much more!