Derek Hough gushed over his sister's engagement to the Washington Capitals hockey player during the Television Academy Cocktail Reception for Outstanding Choreography at the Montage Hotel in Beverly Hills, California, on Sunday, telling PEOPLE, "I couldn't be happier for the two of them."
Hough, 30, and his sister, 27, who were celebrating their Emmy nominations, said he wasn't surprised when Laich got down on one knee.
"I knew that it was happening within the first month they were dating," he said. "It was one of those things where it was instant and that smile and glow she's had hasn't dimmed ever since she met [him]. That's a special thing."
The Dancing With the Stars pro said he's "stoked" about the engagement.
"He's the best," Hough said of Laich. "We went surfing yesterday. We've been hanging out a lot. He's a good guy."
Hough revealed that Laich has already tapped him to be a groomsman in the wedding and said the Canadian handled the entire proposal the old-fashioned way: He asked the talented siblings' father for permission before popping the question!
"My dad and he had a conversation," Hough said. "He's a very traditional guy. I think I recall after they were seeing each other for a couple of months, he actually asked her, 'So can I be your boyfriend?' And she was like 'Wait, I thought you already were.' And he said 'No, we have to do this officially.' He's a traditional guy."
As for the official wedding ceremony? Hough expects it will be "something outdoors, in nature."
"Sentimental. Something special to us. I have an idea where it's going to be," he said, refusing to drop anymore hints. "It's going to be amazing."
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Hough said wedding guests shouldn't expect a special performance, however. For once, he and his sister are leaving their dancing shoes off.
"We perform enough. We've been on two tours," he said. "Me and [Laich] might do something funny. We'll have fun. When my family gets together, they dance anyways. They dance more than me and my sister."