The "Girls" starlet stopped by "Late Night with Seth Meyers" on Tuesday, where she showed off her new diamond sparkler and talked about her surprise engagement.
"I was completely surprised," the actress said of her engagement to "College Humor" co-founder Ricky Van Veen. "The funniest thing about that is I consider myself someone who is impossible to surprise, and yet I am constantly surprised by things. But I walk around the world poised and ready for a surprise."
"And yet a surprise snuck through on you," Meyers said. "A total surprise and the best kind of surprise," she added. "We're really, really thrilled."
So, what does she think of her new bling?
"I'm obsessed with it. I stare at it a lot," the 25-year-old said.
While she offered up no details of how the proposal went down, Williams said making such a huge life decision definitely is a game-changer.
"It feels a little different, as you know," she told the late night host. "It just changes the stakes clearly. It's really fun."
We can't wait to see Allison walk down the aisle!
Check out the clip above to see what else she said about her engagement, and click "Launch Gallery" below to see more celebrity wedding and engagement bling.