JENNIFER ANISTON’s father has finally agreed to walk her down the aisle when she weds JUSTIN THEROUX!

John Aniston had initially dis­approved of former drug addict Justin and got on Jen’s nerves by continually harping about how it was her fault her marriage to Brad Pitt collapsed, says a family insider.

But after a long heart-to-heart – during which Jen, 42, told John that she fully in­tended to marry 40-year-old Justin, with or without his approval – the two tearfully made up and got their father-daughter re­lationship back on track, says the pal.

“Jen wants a dream wedding to Justin, and that includes having her father give her away,” an insider told The ENQUIRER. “So she bluntly told John that he’d have to accept Justin as his new son-in-law if he wanted to remain part of her life.”

John, 78, also had a serious talk with Justin who, as The ENQUIRER exclusively reported in August, has admitted to pals his past addictions.

“When they first hooked up, John was very concerned for Jen’s health and  safety,” noted the insider. “But Justin reassured him he will never go back to the dark side and made it clear how much he loves Jen.”

Jen then sealed the deal by promising John, a star on “Days of Our Lives,” that  she’d make him a grandfather.

 After his heart-to-hearts with both Jen and Justin, John is com­pletely onboard with their plans for a blowout wedding extravaganza in the spring, said the insider.

“Now, the three of them are working on becoming one big happy family, and John’s telling anyone who will listen what a great guy Justin is!”