Stephen accompanied Mel to the Cosmopolitan Ultimate Women Of The Year Awards last night and grabbed former X Factor contestant Ella, 18, for a picture.
However, when he posted it to Twitter and Instagram, Stephen told his followers how excited he was to meet - and "innocently flirt" - with 27-year-old Ellie Goulding (who, incidentally, didn't attend the bash).
"Me and @elliegoulding getting our innocent flirt on!! #funcelebs," he gushed.
Stephen has since corrected his error on Instagram by replacing Ella's handle with Ellie's - but not before several fans clocked his error.
"Cringe!" one wrote. Another said: "Awks!"
Stephen has now apologised for his mistake, blaming his phone rather than his lack of celebrity knowledge. He replied: "Damm u iPhone!!!"
Meanwhile, along with Ella, Stephen and Mel got to brush shoulders with a host of famous faces last night, Little Mix, Kelly Brook and The Saturdays.
Let's hope there was no more confusion over who was who...
Have you enjoyed watching Mel on The X Factor this year? Tell us below, as the best comment from across the website each week wins £50!