Charlie Sheen: I Can't Tell My Twin Sons Apart – Yet

Charlie Sheen: I Can't Tell My Twin Sons Apart – Yet
Brooke Mueller Sheen and Charlie Sheen
Denise Truscello/WireImage

03/20/2009 AT 02:15 PM EDT

They're not identical, but Charlie Sheen's new twins are still managing to fool their dad.

"I can't tell [who's who]!" Sheen, 43, tells Entertainment Tonight from the set of Two and a Half Men just days after wife Brooke Mueller Sheen, 31, delivered twin sons. "They're not identical, but at this stage, they're similar enough."

Their names, on the other hand, aren't giving him any trouble. Max and Bob "are very short and simple – easy to spell and remember," Sheen says. "Bob is the same frontward and backward. I'm a fan of a short and simple name. Max was literally Nick until about a minute before he came out."

Back home in L.A., the new parents are doing well – but are a little tired. "It's pretty amazing. Not a whole lot of sleep, but what parent does at this stage?" says Sheen. "There's adrenaline, excitement, fear."

And the boys already have eager playmates in half-sisters Lola, 3, and Sam, 5, Sheen's daughters with ex Denise Richards. "[They're] thrilled," he says, "but insisting that they're named Bob and Duke. It's not Max, it's Duke."

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