Time flies when you're a mom-and-bride-to-be!

Kate Hudson yukked it up on The Late Show with David Letterman on Wednesday -- the same day she came clean with The Today Show's Matt Lauer about her engagement to Matt Bellamy, father of her unborn child.

"We're getting close -- weeks," Hudson, 32, said of giving birth. "Getting close enough to almost not be able to fly," added the Something Borrowed actress, who had been traveling throughout South America while the rocker, 32, toured with his band Muse. "I don't feel prepared. I can't believe how fast it's gone."

She gushed of her fiance (who gifted her with a 9-carat diamond ring worth an estimated $200,000): "He is a lovely man. English boy. A musician. He's wonderful. I feel very lucky!"

Hudson (who has a 7-year-old son, Ryder, with ex-husband Chris Robinson of the Black Crowes) recounted how she and Bellamy met in 2010. "At Coachella, a music festival. It was a funny time for me, because I was so be single," she admitted.

"Of course that's when you meet this amazing love...Next thing you know you're knocked up!"