Hulk Hogan and his family were "really upset" about the death of ex-WWE star Vader -- with Brooke Hogan and Nick telling us the wrestling star was a big part of their childhood.
"He was always a really nice guy," Nick told us at LAX ... "It sucks. My dad had actually wrestled him a couple of times and they had become friends over the years."
"We got up today and we heard the news and it was kind of somber. Everybody was really upset about it."
Brooke added, "My dad was very sad today."
Vader passed away earlier this week from heart complications after a bout with pneumonia. He was 63.
"We wish all of his family and friends and loved ones the best," Brooke said ... "Any wrestling family is family of ours."