On last night's episode of "Little People, Big World," fans got to witness the heartbreaking loss of Zach and Tori Roloff while still being pregnant with baby Jackson. The episode featured the passing of their beloved dog, Sully, a.k.a. Inspector Sullivan.

LPBW fans know Sully, a Bernese Mountain dog, as Zach and Tori's best friend and loyal pet. Sully was a mainstay at the Roloff Farms and was a huge part of the young couple's relationship. The dog was even a part of their wedding entourage.

Goodbye, Sully

Last March, Zach and Tori were shocked to find out that Sully had an aggressive kind of cancer, which quickly spread to his major organs.

He passed away while Tori was in her third trimester of pregnancy. On her Instagram account, Tori wrote a heartbreaking tribute to their canine friend. She said that Sully's death was the "hardest goodbye" she ever had to make.

During the episode, fans saw how devasted Zach and Tori were while they buried their dog in Roloff Farms. They dedicated the show to Sully, who was only three years old.

Tori's said in her latest Instagram post that last night's "Little People, Big World" episode was difficult for them to film because of their emotions. What's even more devastating for Zach and Tori is the fact that their new baby, Jackson, would not get to meet their dog.

In their latest video blog "Z and T Party of Three," the new parents showed a sweet touch they added to baby Jackson's nursery.

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In Jackson's crib was a stuffed dog that looked like Sully.

"We couldn't resist getting a Sully 'coz he's always with us no matter what," Tori said in the clip.

Hello, baby Jackson!

Zach and Tori welcomed their first child, Jackson Kyle Roloff, last May 12. It was the first grandchild for the "Little People, Big World" family.

With Jackson's arrival, fans are curious to know if the baby also has dwarfism like his grandparents and father. In the TLC reality show, Zach and Tori were seen discussing their apprehensions and fears regarding the baby's health.

There was a scene where Zach was told by the doctors that the baby's ultrasound measurements were indicative that the baby could be "LP" or little person. However, the Roloff family has not made any announcement whether or not Jackson did get his father's dwarfism genes.

Despite Sully's passing, the Roloffs have a lot to be thankful for. Their family is getting bigger, as another baby is on the way. Jeremy, Zach's twin brother, is also expecting his first child--a girl--with wife Audrey. Their little girl is expected to arrive sometime in September. And Molly, Zach and Jeremy's younger sister, is getting married to her fiance Joel this August.

"Little People, Big World" airs every Tuesday night on TLC.