Credit: Jennifer Arnold on Twitter Photo: Katie Couric; William Rijin; and His Adoptive Parents, Jennifer Arnold and Bill Klein

Bill Klein and Dr. Jennifer Arnold have been waiting a long time to welcome a child into their home, and that story will continue to play out this season on The Little Couple, which premieres Tuesday, April 30 on TLC.

We already know there’s a happy ending/beginning since Bill and Jen are now proudly showing off their son William Rijin Klein, age 3, who was born in north-central China on February 24, 2010. The married couple welcomed William home to Houston, Texas on March 5, 2013.

“He’s a really happy guy and has transitioned better than any of us expected,” Jen told the New York Post. “He has the best smile on the planet.” Bill added, “He’s really expressive and can tell you how he wants his burger done just by his eyebrows. He’s got a way with people.”

Bill told People, "I walk into a room and see him and I still can't believe he's ours.” Jen agreed, saying, "We are so deeply in love with him already. It was meant to be." Aww! They explained to People how they came up with William’s name. "When Jen and I met she started calling me Will," he said. "I said, 'My name is Bill,' but at least for a weekend she called me Will until she finally gave up." Jen continued, "It is a family tradition that the oldest boy in Bill's family would be William Walter or Walter William. We can continue part of the tradition but also keep part of his Chinese name and so that's what we decided to do."

Check out another photo of the family on People’s site, featuring William’s truly adorable smile. He is a charmer!

Sources: New York Post, People