Last year, Marvel Comics announced the Wedding of the Century, with no more detail given. Fans have been making assumptions and have theories such as that the wedding would not be from main characters but now a major mutant proposal has been revealed in X-Men Gold 20.
After Kitty Pride and Colossus were trapped in a life or death situation, Kitty decided to stay and save Colossus life instead of running away. Kitty then evaluated the situation and considered that there is no time to lose and popped the question.
Even with these given facts, we cannot know for sure if this is the famous wedding that was announced, because the issue ends before Colossus gives an answer to Kitty.
Kitty and Colossus have one of the longest relationships in the Marvel world and they have talked about marriage in the past but more as a way for Colossus to show his level of commitment. However, the road has not been easy, they broke up twice, she was committed to Star Lord and Colossus for his part fell for someone else during the original Secret Wars.