Rob Kardashian, 29, and fiancée Blac Chyna aren't just expecting one baby — they're going to be welcoming twins!

A source tells Life & Style that the couple is making room for two bundles of joy, who are due this fall.

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“[Chyna] knew almost immediately that this pregnancy was different because of how fast her body was expanding and changing,” the insider reveals of the 28-year-old, who is already mom to three-year-old son King Cairo.

So how did Rob's famous family react to this latest development? "[Kris Jenner] has expressed her joy over the twins, telling Rob, ‘the more the merrier.’”

For more on the pregnancy, pick up the latest issue of Life & Style, on newsstands now!

l&s cover

And for a closer look at Chyna and Rob's whirlwind romance, scroll through the gallery below!