Illogical Feelings

McCoy's eyes widened. “I must be wrong!” He said. “It just...it looks like that necklace of Spock's mother. The one she gave him, to remember him by. I saw it in his quarters but... there must be thousands like it. This cannot be the same!” He let out a laugh. “Why would I have Spock's necklace?"

This time, it's not Spock who goes to the alternate timeline but McCoy and with him, he takes a token of Spock's affection, who, in the future, is in fact his husband. When the younger versions of Spock, McCoy and Kirk find out, a bit of a crisis ensues, but maybe also something that should have happened a long time ago.