LOS ANGELES, May 25: Longtime Fox television executive Mike Darnell, who helped shepherd “American Idol” to the top of US TV ratings, will leave the network, Fox said yesterday, after the network lost its lead among the younger audience most appealing to advertisers. Darnell, 51, the network’s president of alternative entertainment, oversaw some of Fox’s most popular shows – including talent contest “The X Factor,” animated series “Family Guy” and reality cooking shows “Hell’s Kitchen” and “Kitchen Nightmares.” (agencies)