According to new reports, the film producer put a lot of thought into the design of the elaborate ring and had had it ready for months but was waiting for the right time to propose.
Matt, who has been with Christina for three years, popped the question while the lovebirds were spending a romantic Valentine's weekend in Hawaii.
"Matt spent over a year designing the ring with the ring designer to represent their three-year journey together as a couple," an insider told People. "He has been planning this for a while.
"He took two of Christina's favourite rings to design something that incorporated [both designs] into one, similar to both their lives coming together as one."
The different stones on the intricate ring represent different aspects of Matt and Christina's relationship.
"Every single placement of each stone has a reason and meaning," the insider added. "The actual band weaves and intertwines [the] diamonds. Every connecting criss-cross symbolises how their paths crossed."
The rock also features nine special multi-colour gemstones underneath the band that aren't visible when the ring is worn.
"They all symbolize something meaningful to the couple. Christina is very spiritual and having the stones touch her actual skin will emit positive energies surrounding her at all times. They represent things like love, protection and healing."
Christina, 33, announced her engagement on Saturday when she took to Twitter to show off her glittering new ring.
"He asked and I said," wrote the Beautiful singer, with a picture of her diamond-adorned hand holding Matt's in front of a romantic beach setting.
Christina's tweet was swiftly retweeted more than 5,000 times and prompted a host of congratulations from her followers.
Matt and Christina met on the set of 2010 movie Burlesque. At the time, the mother-of-one was in the middle of a painful breakup with her ex-husband Jordan Bratman.
Christina and Jordan have a son Max Liron Bratman together.
Over the past three years Matt has become close to Christina's six-year-old Max and the trio live together in Los Angeles.