After this slip-up, Armie Hammer may, er, take a hammering from his pregnant wife, Elizabeth Chambers.

The Birth of a Nation star, 30, and the actress, 34 — already parents to daughter Harper, 21 months — are expecting a boy next year, Hammer accidentally revealed on Jimmy Kimmel Live Thursday, September 29. Watch what he said in the clip above!

Though they intended to keep the gender under wraps, Hammer hinted to the host that he would no longer be outnumbered at home.

“You can find out now at nine weeks, which is really bizarre,” he said of gender testing. “They do a blood test. It’s crazy. They test if there’s hormones in there. They go, ‘Oh, you’ve got testosterone.’ So you either have balls or you’re having a baby boy.”

When Kimmel asked about potential names — “When your last name is Hammer, you really have a wide variety of options,” he joked — Hammer offered up some possibilities … but only for a baby boy.

“We’re thinking Jack, Jack Hammer,” he joked. “Michael Charles and he can just go by M.C.” Suddenly he realized his mistake. “I think I just gave away our baby name,” Hammer revealed. “I’m in so much trouble!"

Sure, he may be stressing over his blunder, but daughter Harper has no worries about her upcoming role as a big sister. “She loves it. If you go, ‘Where’s the baby?’ she’ll rub Mama’s belly and kiss her stomach. It’s really cute,” gushed the Social Network actor. “I don’t know if our daughter has been easy or if we’ve just been winging it in the right way, but we haven’t had too much of a plan and it’s all kind of gone alright.” 

Dressed and ready for the premiere of #Freefire. And the premiere of baby Hammer Number 2!

A photo posted by Elizabeth Hammer (@thisisechambers) on

Hammer and Chambers announced the pregnancy on Instagram September 8 while at the Toronto Film Festival. “Dressed and ready for the premiere of #Freefire,” she captioned a shot of her husband cradling her growing bump. “And the premiere of baby Hammer Number 2!”

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