The 'Ace Ventura' actor is reportedly set to pop the question to his 30-year-old student girlfriend any day now.
A source said: "Jim is going to propose! He's absolutely crazy about Anastasia and couldn't be happier."
Twice-married Jim - who dated glamour model Jenny McCarthy for almost five years before splitting in 2010 - is said to have realized he was ready to marry again when he turned 50 in January - and believes Anastasia is the one for him.
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The insider told Star magazine: "[She is] really smart, but what he likes best about her is her sense of humour. She makes him laugh.
"Jim confessed to Anastasia, 'It's not always easy being with me, in more ways than one'. But he added, 'I promise to make it worth your while'."
The father-of-one was previously married to his 'Dumb and Dumber' co-star Lauren Holly from 1996 to 1997, and to actress and waitress Melissa Womer from 1987 to 1995. They have one child, daughter Jane, 24, together. He has also dated 'America's Next Top Model' star Anchal Joseph.