"Things got really bad between them and then she pops up pregnant," a source tells PEOPLE.
Hartwell, 38, made the separation legally official from The Cosby Show alum earlier this week – just six months after the couple wed and one week after the actress announced she is expecting.
Now, a source close to Hartwell tells PEOPLE the former NFL star "doesn't have any evidence of her cheating" but wants a paternity test because he is concerned about the timing of the pregnancy.
"It's just that he had told her he wanted to wait before having a baby and things got really bad between them and then she pops up pregnant," says the source.
"He even told her he didn't want to release the bump picture so soon, but she did it anyway," adds the insider.
The source also says that Hartwell, who has a son from a previous relationship, "just wants to make sure that just because they were married he still covers his bases and gets everything checked out."
"The pregnancy came during a very dark spot in their relationship," explains the source.
Pulliam, 37, announced her pregnancy last week on Instagram.
"Surprise!!! We have a new addition coming soon... Tune into #KandidlyKeshia this week for the details!!" she captioned a picture of herself posing with a cupcake topped with pink frosting, revealing she's expecting a girl.
The pregnancy news came just a few months after Pulliam and Hartwell tied the knot in January following their New Year's Eve engagement.
"It was my dream," she said of her wedding during one of her podcasts early this year. "We did it literally in our living room in our home. We come from large family. I'm one of four. Ed is one of six. We invited people. They had no clue they were coming to a wedding. They thought they were coming to a New Year's party."
This story originally appeared on PEOPLE.com.
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