The Big Bang Theory star has said that she was completely surprised by her handsome beau's proposal as he "actually started a little fight with me and threw me off."
She adds: "I was like 'Oh my God, things aren't great.'"
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But the 26-year-old's decoy went perfectly to plan. "He surprised me at the end of the night ... [when] he popped the ring out. It was amazing," she told Entertainment Tonight, speaking from the set of her new film The Wedding Ringer.
The actress also revealed that, while the pair got engaged following a whirlwind romance of just three months, "From day one I just knew immediately and it's been magic.
"We have all the same family friends. We grew up with the same people, we just never met. So I kind of feel that I've known him my whole life. I know that it seems a little crazy on paper, but it's what works for us."
Ryan is said to have popped the question on Wednesday of last week, days after the happy couple made their red carpet debut at the Emmy Awards.
His fiancée was spotted soon after wearing a diamond engagement ring on the set of her appropriately-named film, The Wedding Ringer.
"It's only been three months but she knows Ryan is the one," a source told US Weekly. "When you know, you know."
Kaley, 27, hinted at her joy when she tweeted soon after, "Flying high, I could literally touch the sky with you…."
Like her husband-to-be, Kaley was once a nationally-ranked amateur tennis player, but she retired when she was 16. The sporty actress is now an avid equestrian and owns four horses.
Prior to meeting Ryan, she had a brief romance with Man of Steel's Henry Cavill, and she secretly dated her Big Bang Theory co-star Johnny Galecki for two years.