A family feud has erupted on the “Duck Dynasty” set because patriarch PHIL ROBERTSON is jealous of his brother SI’s popularity, an insider told The ENQUIRER.

“Phil is just plain fit to be tied that Si has become the most favorite Robertson with fans of the show, and it’s driven a wedge between them,” the source revealed.

Si has captivated America with his backwoods philosophies and quirky humor – and his book “Si-cology 1: Tales and Wisdom from Duck Dynasty’s Favorite Uncle” has joined Phil’s “Happy, Happy, Happy: My Life and Legacy as the Duck Commander” on the best-seller list.

But the tension exploded after A&E execs floated the idea of Si getting his own spinoff TV show – and he decided to think it over.

“When SI didn’t immediately reject the idea, Phil blew a fuse because he’s got plans to ditch A&E altogether and do his own show where he can preach the gospel all he wants without producers interfering,” explained the source.

As The ENQUIRER reported, Phil’s strategy included blasting gays in a magazine interview in an effort to get out from under the fam­ily’s long-term contract with A&E. It almost worked, as the network suspended him from the show in­definitely. But after an uproar over Phil’s free speech rights – and the fact that the “Duck Dynasty” show and merchandising brought in a whopping $885 million last year – Phil was reinstated.

But some damage was done. The Season 5 premiere on Jan. 15 drew 8.5 million viewers, down from the  nearly 12 million who tuned in to the Season 4 premiere last year.

“I don’t think Phil’s comments drove away viewers,” said the source. “They’re more upset over the way producers manipulate the image of the family.”

Even though Phil, 67, agreed to return to the show, an insider told The ENQUIRER that he’s still planning to form his own TV pro­duction company and find a legal loophole in the A&E contract so they can all jump ship, possibly to a Christian broadcasting network.

“Phil’s already rich and not interested in money, he just wants to have more control over his message,” explained the source. “But now Si is throwing a monkey wrench into his plans by considering A&E’s idea of him doing his own show.”

Ironically, Si, 65, wasn’t even supposed to be on “Duck Dynasty” in the first place.

“He tagged along to one of the meetings with A&E producers and they really liked his person­ality,” said the source. “So they decided to sign him up. Then his popularity just took off, and that got under Phil’s skin. The feud is actually quite troubling to both of them. Phil is Si’s big brother and has always looked after him. When Si came out of the Army after 20 years and really didn’t have any direction, Phil hired him to work for his Duck Commander business.

“For now, everyone’s just hoping they can make peace.”