Casper Smart let the big news slip while promoting his new Tv show A Step Away on E! News on Friday (16Aug13).
When asked if his girlfriend would be joining Keith Urban for the 13th season of the show, he simply said, "yes".
Reports suggest the dancer was under the impression the news item had already been released by the talent show's producers.
Last month (Jul13), Fox Network President Kevin Reilly revealed Idol bosses had been in negotiations with Lopez, who served as a judge alongside Randy Jackson and Steven Tyler for two seasons on the show before stepping aside to concentrate on touring and acting last year (12).
Tyler also stepped down and their spots were filled by Urban, Mariah Carey and Nicki Minaj. Jackson, Carey and Minaj all quit the show at the beginning of the summer (13). Urban announced he would be returning in July (13).