Shepard surprised Bell with an unconventional gift: A sloth. Bell told DeGeneres, "My entire life had been waiting for this moment, where I would get to interact with a sloth."
The "House of Lies" actress explained in the interview, which can be seen below, that Shepard told her to go to their back room to wait for her birthday present.
"I immediately was overcome and thought, 'There's a sloth near,'" she told DeGeneres. "And I didn't know how to process that."
"First thing you should know about me. If I'm not between a three and a seven on the emotional scale, I'm crying," Bell added. "I'm crying if I'm too sad or if I'm too excited. Always."
Bell continued, "So I am sitting on my bed, knowing that a sloth is here ... I start to have a full fledged panic attack. I don't know how to compete with all this emotion so I just kind of crawl up on the bed and I'm crying so hard."
Shepard caught her reaction on camera, which was then showed to the audience. Bell is seen crying on a bed covering her face while Shepard tries to comfort her.
The actress explained the sloth stayed for her birthday party. "I mean I needed to be sedated, clearly," Bell said.
Bell and Shepard announced their engagement in February 2010 after appearing in the romantic comedy "When in Rome" together.
Shepard plays Crosby Braverman on the comedy show "Parenthood" and has appeared in movies such as "Idiocracy" and "Baby Mama."
Bell, who previously starred in "Veronica Mars," currently stars in "House of Lies" with Oscar nominee Don Cheadle. In the series, which premiered in January, Cheadle plays Marty Kaan a member of the management consultant team that includes Bell as Jeannie van der Hooven. The two work for the No. 2 ranked consulting company with an office in Los Angeles but travel to projects around the world.
"Every 'Frontline,' every '60 Minutes' is about who is screwing who at the top of the food chain and I feel like it's about time that someone showed that underbelly in a sort of sophisticated, sleek way," Bell told OnTheRedCarpet.com about the series recently. "Don Chaedle's attachment didn't hurt as far as being attracted to the project because I think he's so spectacular."
Check out Kristen Bell's interview on "The Ellen DeGeneres Show" below.