Nick Offerman and Megan Mullally share their 15-year love story in new book "He treats me like a queen, he does," Mullally said.

"Parks and Recreation" alumni Nick Offerman and Megan Mullally are revealing details behind their romance in a new book, "The Greatest Love Story Ever Told: An Oral History."

The couple stopped by "Good Morning America" on Monday after recently celebrating their 15-year wedding anniversary. Offerman said his gift to Mullally was made possible thanks to Krystal Nielson and Chris Randone of "Bachelor in Paradise."

"I make things when I can for Megan, and there's a traditional list of materials for anniversary gifts," Offerman said. "First anniversary is paper and so-forth. Fifteenth anniversary is crystal, so we're fans of 'The Bachelor' television program. It's a popular TV show."

He went on, "There's a super-heroic character named Krystal on that program, and so she and her paramour, a guy that goes by the name of the 'Goose' -- 'Team Glitter Goose' -- they recorded a happy anniversary video for Megan."

Mullally spoke about whether it was love at first sight for the comedic pair who married in 2003.

"It was for him," she joked. "We met doing an equity-waiver play in Los Angeles, and Nick was the only person who spoke to me the first day of rehearsal. He said, 'Hello this is going to be fun,' and I said, 'Wow, thanks for talking to me.'"

"All the guys I dated up until that point had been very muscle-free, androgynous rock drummers ... and then this came along," Mullally added. "We've never been apart for more than two weeks. I think it's very helpful."

As for how they make it work, Mullally had a sweet response.

"It's one thing to be in love and love someone, and it's another thing to like them," she said. "And I just really like him. I like listening to him talk. I think he's funny; I think he's interesting; and he's a great person. He's a great man. He treats me like a queen, he does."

Offerman chimed in, "We're lucky that we found each other."

"The Greatest Love Story Ever Told" is out tomorrow.