RadarOnline.com has learned that Jost has moved some of his possessions into her New York home and is spending time with her 3-year-old daughter Rose.
The actress was also linked with agent, Kevin Yorn, but it seems that Jost has won her over.
But friends have told her to be careful because she might infuriate estranged husband Romain Dauriac who wants full custody of their child.
The source revealed: “Scarlett wasn’t planning on getting serious so soon, but Colin’s swept her off her feet!”
“He’s moved a bunch of his stuff into Scarlett’s place, and she’s given him a key.”
“Scarlett’s being coy about how much time she spends with Colin,” added the source.
“But Romain’s not stupid, and he’s more than willing to use Scarlett’s evasiveness in a custody battle. Romain thinks it’s irresponsible for Scarlett to have another man around Rose permanently.”
However, it’s understood that the 32-year-old Avengers star has fallen quickly for Jost, 35, after her marriage to French journalist Dauriac imploded.
Dauriac, 34, expressed his shock earlier when his wife filed divorce papers at a New York court saying the marriage was "irretrievably broken."
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