So, he worked with Daniel Arik of Happy Jewelers and Newport Jewelers to create a one-of-a-kind piece.
"He did have an idea of what he wanted," Arik told ABC News. "We showed him a few different pieces and custom made his ring."
McCarthy, 41, revealed the couple's happy news on Wednesday's "The View." After tearing up while explaining the details of the proposal, she flashed her ring, which Arik called "one-of-a-kind."
The "Blue Bloods" star said that McCarthy preferred a colored stone to a diamond. In the end, he chose a 10-carat yellow sapphire surrounded by nearly two carats of diamonds, set in white gold.
"Yellow sapphire is really expensive, especially in that size," Arik said. "You don't find many people buying a 10-carat yellow sapphire!"
When Wahlberg laid eyes on the finished product, "he went crazy," the jeweler recalled.
"It was really nice. When he saw it, he was stunned," he said. "The experience was amazing. Out of all the people I deal with, he was one of the easiest, most pleasant people. It was really fun."