Million Dollar Listing 's Josh Flagg Shares How He Helped Tori and Candy Spelling Mend Their Relationship

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After year's of family tension, Candy and Tori Spelling have finally been able to find peace in their relationship with a little help from mutual friend Josh Flagg.

"We had dinner up at Candy's house," the Million Dollar Listing Los Angeles star, 37, tells PEOPLE exclusively. "The whole family came — the kids, everybody. We had the most amazing evening. We screened Troop Beverly Hills in the theater, which is fun for the kids, because her mom was in that movie obviously."

"They were hugging and crying," he continues. "I'm not saying the next day everything was back to normal, but I'd say over a couple weeks maybe, slower and slower, it just got back to normal."

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The relationship between the Beverly Hills 90210 alum and her 77-year-old mother grew more strained than ever after her father, Hollywood producer and director Aaron Spelling, passed away in 2006. Tori claimed to have found out about her father's passing via email and was left only a fraction of his $500 million estate. Candy, on the other hand, seemingly struggled to accept her daughter's relationship with Dean McDermott, to whom she's now been married for 16 years.

Both women aired out their grievances publicly over the years in memoirs and interviews.

RELATED: Tori Spelling Says Her Relationship with Mom Candy 'Is Really Good' After Years of Estrangement

"Tori and I are a work in progress and probably always will be," Candy wrote in 2013's Candy at Last. "I notice that the more my self-esteem expands, the less patience I have for the pursuit cycle she creates when she shuts me out. We have a pattern, and until we can break it hand-in-hand, this is going to be the little dance she and I do together."

For her part, Tori told PEOPLE in 2009 when she and Candy were not on speaking terms: "I love my mother. I've always loved her [and] no doubt she loves me. There's no feud. We simply never meshed. My mother is who she is. I've become who I am. At some point I realized those two just didn't go together."

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Flagg, who's known the family for years, spoke to both parties separately and realized both wanted to be in each other's lives. Feeling it was all a giant misunderstanding, he jumped in to help — with a little cosmic push from Aaron himself.

"I was sitting at dinner one night with Candy," Flagg shares. "It was really sweet. We went to Musso & Frank's [in Hollywood] and Aaron's star is right outside [on] the sidewalk. She took me outside and she goes, 'Aaron, I want you to meet my friend Josh,' and I said, 'Hello, Aaron, pleasure to meet you. I've heard a lot about you.' So we went inside back for dinner, and I just started talking."

He adds, "I'd always heard Candy's opinions, and I'd heard Tori's opinions, but they both really love each other very much. I mean, they're mother and daughter. I was just listening, and I was like, 'This just sounds like miscommunication.'"

After "a couple of years" of not talking, Flagg engaged the two in communication and got the two together for lunch to hash things out.

"This is the simplest deal I've ever negotiated," Flagg jokes. "It was as if nothing ever changed."

RELATED: Tori Spelling Says She's 'Really Happy' in Relationship with Mom Candy: 'We Text Every Single Day'

While that "deal" is closed, Flagg is excited to share his tips with readers on how to close their own in his newest book The Deal: Secrets of Mastering the Art of Negotiation.

"It just gives really great examples of what to do and what certainly not to do," Flagg teases. "And all the things I would've loved to have done differently, if I'd had the chance — or just to look back. It's very self-deprecating. It makes fun of myself. I think it's a really easy read."

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The Deal: Secrets of Mastering the Art of Negotiation is available now everywhere books are sold, and Million Dollar Listing: Los Angeles premieres Dec. 8 at 9 p.m. ET on Bravo.