EXCLUSIVE: Joanna and Chip Gaines Reveal How They Keep the Spark Alive After 13 Years of Marriage

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ET was with Fixer Upper stars Chip and Joanna Gaines as they celebrated their 13th wedding anniversary in New York City's Central Park, where we got the couple to share what it takes to have a successful marriage.

"One of the secrets to our marriage, or the success of our marriage, is just really caring about one another," Chip told ET.

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Fans of their HGTV show know how well the couple gets along and now they've detailed their love story inside the pages of their new book The Magnolia Story.

In the book, Joanna shares how Chip proposed to her by bringing her to a jewelry store owned by a family friend, where Joanna was able to design her own engagement ring. Twelve years later, when the couple was able to afford a better diamond, Joanna decided to not to replace the stone, saying, "This is the original diamond I picked, and it's perfect just the way it is."

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It's their frugality that seems to have been one of the secrets to their financial success.

"Our idea of splurging is going to a full-priced meal without a coupon," Chip said. "That's our idea of 'Hey we're going for it! We're not even going take the coupon with us tonight!'"

As the proud parents of four children, all that budgeting could come in handy, especially if Joanna gets her wish of having two more children.

"You wish," Chip said.

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Fixer Upper airs at 9 p.m. ET/PT on HGTV.