In X2:X-MEN UNITED a new mutant was introduced- 'NIGHTCRAWLER', the amazing blue coloured teleporter. Initially he was being controlled by WILLIAM STRYKER, the man responsible for WOLVERINE's ADAMANTIUM skeleton.
For a normal non-geek fan, NIGHTCRAWLER looks like MYSTIQUE, but acts like AZAZEL from X-MEN:FIRST CLASS. For those of you who do not know, this guess was made by many newbs, but turned out to be correct. Their guess was confirmed by X-MEN:DAYS OF FUTURE PAST. While MYSTIQUE sees an autopsy report, belonging to AZAZEL, see almost cries. This meant that AZAZEL and MYSTIQUE had a romantic relationship, and she was pregnant during the happenings of DOFP. Moreover, she must have known that BOLIVAR TRASK had captured AZAZEL, leading to her dislike towards him and his attempted assassinations.
By knowing the relationship between the two red and blue mutants, we can confirm that NIGHTCRAWLER indeed is their son, just as he was in the comics. He has gained her mother's appearance, and his father's abilities. But unlike both he has good in him, and is a vital part of the X-MEN in the comics.
In the upcoming X-MEN movie, sequal to DOFP, we will be seeing Kodi Smit-McPhee as NIGHTCRAWLER.