Katharine McPhee is dating her Scorpion costar Elyes Gabel, Us Weekly can exclusively confirm -- get the details on their sexy new romance Credit: Ethan Miller/Getty Images

What a smashing surprise! Katharine McPhee is dating her Scorpion costar Elyes Gabel behind the scenes, Us Weekly can exclusively confirm.

McPhee, 30, and the British actor, 31, had eyes (and hands) only for each other when they were photographed kissing between takes on the L.A. set of their freshman CBS series on Aug. 15. The American Idol alum went in for a peck on the cheek as she playfully grabbed Gabel's butt.

The intimacy continued when the new lovebirds were joined by the rest of their cast for a private premiere of the show at nightspot Warwick in Hollywood on Sept. 22. Although they didn't arrive together, they "were inseparable and got cozy all night," an insider tells Us. McPhee let loose and danced around the club with her friends during commercial breaks too, the source adds.

The new relationship comes nearly a year after McPhee was caught kissing her Smash director Michael Morris in L.A. At the time, both McPhee and Morris were married: she to producer Nick Cokas, he to actress Mary McCormack, with whom he shares three young daughters.

"She is so embarrassed she was caught," an insider told Us at the time. "She should have known better!" 

McCormack briefly kicked Morris out of the family home in the aftermath of the scandal, but the spouses of 10 years eventually reconciled. McPhee's attempts to mend her marriage, however, fell through; this past May, she filed for divorce from Cokas, 49, after six years of marriage. A rep for the actress told Us that the exes "have an amicable relationship and will remain friends."