The former talkshow host, who began dating Evans in summer 2010, announced the news via her Twitter page on Thursday.
"Thrilled to share some happy news with you..... I'm engaged! :)" Lake wrote on the social networking site. "The cat is out of the bag. Phew! I'm terrible at keeping secrets. :)"
Lake also attached a photo of herself and Evans on holiday, where Evans is said to have popped the question.
"Yes, she is engaged," Lake's rep told US Weekly. "[Christian] proposed while they were on vacation in Spain."
Lake was previously married to Rob Sussman, with whom she has two children. The pair divorced in 2003.
She recently said that she is "totally in love" with Evans and that he makes her "happier than she's ever been".