Derek Hough is remembering the late Len Goodman.

Days after the beloved Dancing With the Stars head judge died at age 78, the pro-dancer-turned judge got emotional reflecting on their friendship.

"We knew he was unwell but we certainly didn't know the extent," Derek, 37, said on the Whine Down With Jana Kramer podcast April 30. "This was a huge shock to all of us and it's incredibly sad."

And as they process their grief, members of the DWTS family have turned to one another for support.

"We've had countless tears and phone calls with colleagues and friends. Most of it is just sharing how much we just love the guy and how lucky we are and how lucky we were to spend as much time with him as we did" Derek said on Whine Down, later adding, "He's a special man."

Len passed away April 22 after a quiet battle with bone cancer and six months after he retired from DWTS after 17 years and moved back to his native England. Following his death, many of his former co-stars, including fellow judges Carrie Ann Inaba and Bruno Tonioli, shared tributes to him on social media.

While Len and Derek became colleagues when the latter joined the show as a dance pro in season four, they had actually met a decade before.

"I had the pleasure of knowing Len since I was 12 years old," Derek said on Whine Down, "when I lived in London."

At the time, Derek and his sister Julianne Hough were studying dance in England with DWTS alum Mark Ballas and his parents, dance coaches Shirley Ballas and Corky Ballas.

Derek, who spent the last four seasons as a judge on the competition series, also noted what this past year with Len meant for him.

"I really savored the moments I spent with him," Derek said. "We were playful with each other and we had these one-on-one conversations."

In fact, the time was so special that Len left Derek sweet parting gift ahead of his final DWTS episode.

"There was this giant picture of Len, framed, beautiful gold frame," he recalled. "It had this handwritten message from him and it was so beautiful but also [had], like, inappropriate humor. And it was signed by him...I was just so touched and moved by that, just thinking about how our lives are so entwined."

Derek plans to pay tribute to his late friend and colleague on his upcoming Symphony of Dance tour. "There will definitely be some moments of honoring him and tipping the hat to him, without a doubt, on tour," he said, "I think not only just for us but I think, honestly, for the audience."

And he knows the people coming to the shows, which begin this fall, feel the same way about Len.

"I think a lot of the audience that will come to the show, they're also, in a way, mourning this guy that they watched for 20 years on TV," Derek added. "He's Len Goodman. He's the head judge. He's the guy that we all love."