‘AMERICAN Idol’s” return Monday night drew one of the biggest audiences of the TV season – and took Fox’s new reality show, “My Big Fat Obnoxious Fiancé,” along for the ride.

The third-season opener of “Idol” averaged 29 million viewers – easily the night’s most-watched show.

A good chunk of the “Idol” audience stuck around for “Fat Fiancé,” which snared 19.6 million viewers – the highest-rated series premiere on any network in over a year. “We’re thrilled – to get this kind of number for a brand-new show is just great,” Fox reality chief Mike Darnell said.

On the show, a young woman is trying to dupe her family into thinking she’s marrying a guy she met on a reality show. If she gets through the wedding ceremony, she wins $500,000.

What she doesn’t know is that the over-the-top, belching, mannerless Steve is really an actor.