The couple, who are a part of the band Alexander Jean, have been together for over three years.
Mark secretly asked BC to marry him the day before Thanksgiving! “She’s wearing an engagement ring.” Mark proposed in Nov.
"It's just so special with Bindi," he told reporters backstage.
"She's a champion of life."Bindi shared the same sentiment, telling those in the ballroom that she gained another brother in Derek.
This  is something completely new to me."Mark adds, "For me, it's very cool to celebrate winning a medal, but the road to that medal is hard and taxing.
“They all fool around with each other,” the insider says.
In case you needed further proof that the two are friends for life, consider this: Derek's hopping on a plane to Australia in a couple weeks "to tackle crocodiles and get my official khakis!
"The Houghster may have nabbed his sixth Mirrorball trophy, but it was his partnership with Bindi that undoubtedly made it his favorite season.
They trained in ballroom dancing in Europe together and lived together for years as kids.
As adults we have seen them present themselves as best friends and even took their acoustic band on the road to play some gigs. But do men that are pushing 30 buy a comfy home in the Hollywood Hills together?
(In case you missed it, you can read our recap of the best and worst moments here.)Almost an hour after Tom Bergeron declared Bindi Irwin and Derek Hough the winners of season 21, Bindi was still in disbelief, shouting from the top of her lungs, "I think I'm going to scream for 20 minutes!