Ellen DeGeneres throws Jennifer Aniston an impromptu birthday party for the 'He's Just Not That Into You' star's 40th birthday!

It happens on Friday, so tune in to "The Ellen DeGeneres Show" when the talk show host presents Jennifer with a red velvet cake - and asks her how she feels about turning the big 4-O.

"I have to say really, I feel better than I ever felt in my life," she tells Ellen. "I did have a moment, though, over the weekend. My first like, 'Huh ... I don't want to (turn 40)'. I found a really long gray hair and it kind of flipped me out. It's not my first but it's the fact that it was so long. I was like, 'Oh, how many others are there and what does that mean?' It actually brought me to tears slightly."

Jennifer also shares that Courteney Cox and David Arquette will be attending a small party she is having on Saturday for her birthday, but for now that is the only "Friends" reunion she has planned.

That said, she tells Ellen, who takes Jennifer on a visit to a reconstructed "Central Perk" set, that she would be willing to do "Maybe…Like one (episode of 'Friends')."