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Gigi and Bella Hadid won't be getting any little siblings ... their dad and his fiancee called it quits in part because they couldn't agree on starting a family together.

Sources close to Mohamed Hadid tell TMZ ... he and Shiva Safai parted ways about a year ago -- even though she didn't confirm it publicly until this week. We're told the 39-year-old absolutely wanted to be a mom, but Mohamed wasn't looking to go down that road again.

As you know ... Mohamed is already a father to 5 beautiful children -- daughters Bella, Gigi, Alana and Marielle, and son Anwar.

Another reason for the breakup, sources close to Shiva tell us, was her reaction to a woman who publicly claimed she had a relationship with Mohamed. We're told it made Shiva reevaluate things, before having a heart-to-heart with him about their future.

It's still unclear who broke up with who, but we're told Mohamed and Shiva both agreed they were on different pages.

The now-exes got engaged way back in 2014, but we're told he came to the realization he didn't want to be married again -- he's already got 2 under his belt.

Our sources say he hopes Shiva can find Mr. Right, get married and have kids.

One last bit of accounting ... the ring. We're told Shiva's engagement rock is a Hadid family heirloom, and she gave it back to Mohamed, and he's passed it on his eldest sister.