Pregnant Kelly Clarkson is blaming wild womanizer Blake Shelton for a bimbo eruption that’s caused her new hubby Bran­don Blackstock to be branded a serial cheater!

Sources say the crisis has thrown Kelly’s months-old marriage into turmoil, and the “Stronger” singer has turned to her stepmother-in-law, country music legend Reba McEntire, for advice.

“Kelly can’t believe that Brandon is cheating, but she knows Blake is a major partier and womanizer,” said an insider.

“Brandon is Blake’s manager, and now that she and Brandon are start­ing a family, Kelly doesn’t think it’s a good idea for him to be hanging out with Blake.”

The “Voice” mentor, who was or­dained through an online ministry, was set to officiate at the couple’s marriage ceremony. But Kelly, 31, and Brandon, who turns 37 this month, decided to elope instead, and tied the knot on Oct. 20. As The ENQUIRER recently reported, the couple has moved into an opulent $2.86 million mansion in Henderson, Tenn.

But now Kelly’s worried that Blake’s partying – which has triggered problems with wife Miranda Lambert – could cause the same troubles in her marriage, sources say.

As The ENQUIRER has reported, pals say Blake and Miranda’s three-year union is headed for divorce after being repeatedly rocked by allega­tions of Blake’s wandering eye.

Desperate to avoid the same heart­ache, Kelly sought the advice of Brandon’s stepmother, country queen Reba McEntire, said another source.

“Kelly is terrified that Blake might corrupt Brandon,” said the source.

“Reba didn’t want to believe Bran­don would even look at another woman, but she advised Kelly to read him the riot act right now.”

For Kelly, red flags went up when an unidentified woman told a website she’d been involved with Brandon, who has two kids with his ex-wife.

“Brandon has been cheating on Kelly (with me) for the past 5 months,” the woman wrote on Dec. 2.

“We met at a golf club in TN and have exchanged multiple texts and hung out a few times over the last little while. We haven’t slept togeth­er but we’ve been intimate in other ways.”

Then, a second woman claimed she’s expecting Brandon’s child after they hooked up when he was with Blake in L.A.

Kelly blasted the claims as “false rumors” and “absolutely absurd” on her Twitter feed, explaining that the woman who posted “this fictitious rumor about my husband” used to be her personal assistant until “I termi­nated her for trying to steal from me.”

But behind the scenes a furious Kelly – who performed live on “The Voice” on Dec. 3 despite suffering morning sickness – is blaming Blake for dragging Brandon into his sexu­ally charged lifestyle.

“Kelly has laid down the law and told Brandon to cool it with Blake,” said the insider. “From now on, he’s on a short leash.”