Yesterday Star magazine broke the story that Charlie Sheen has walked out on his wife Brooke Mueller, who happens to pregnant with twins, and now the Tabloid is claiming that Jennifer Aniston is trying to get pregnant with twins by John Mayer. Take that Angelina Jolie!

Jen has been undergoing fertility treatments, determined to have a pair of babies with John. As we told readers earlier this year, Jen's biological clock began ticking so loudly that she had some of her eggs frozen just in case she didn't meet Mr. Right in time. But now that she's proposed  to John -- as Star also reported -- and he's excited about being a dad, she's doing everything she can to conceive before her 40th birthday in February. She's even been having alternative medicine treatments to increase her chances of having twins.

"She knows her baby-making years are limited," says a source. "It's hard for her to think of anything else -- she has babies on the brain!"

The celebrity magazine goes on to say that Mayer is so fired up to be a father that he's gone on an spending spree to get ready!

"He ordered a bunch of books on Amazon about pregnancy and parenting," another source reveals. "He's just as eager as Jen is. They've discussed how they plan to raise their kids, and they agree on mostly everything. They can't wait to be parents together."

Since I'm not a chick, I don't have a womb. Nor do I have any kids so this whole birthing thing and the fertility game is completely foreign to me but does receiving fertility injections actually increase your chances of giving birth to twins?

And do you really think Jen wants to have a baby? With John Mayer? To get back at Brad Pitt?