McCoy was in the transporter room when Scotty beamed Spock and Jim up, and knew at once that something between the two had changed. At first sight all looked normal, but he knew Jim long enough to see that Jim was happier than McCoy had ever seen him.
None of them said anything, though. The first thing he did, was ordering Jim to sickbay to treat his head wound.
"How did you get this, anyway?" he asked them when he was finished.
"Dunno. Something hit me on the head. But it's not bad."
"Are you the doctor now?"
"I walked up and down that mountain, the headache is gone, so yeah, I know there is nothing wrong."
"You're full of love-hormones. That's why you don't feel any pain," McCoy answered. It was meant as a joke, but he could see that he had touched a nerve.
"How do you know that?" Jim asked him, wondering how his friend had found out. He knew that Spock hadn't told neither McCoy nor anyone else on the ship about what happened before he and Spock were beamed up. So how the hell did he figure that out?
"Know what?"
"You know, that... Spock and I..." Jim started.
"Thank God in heaven. Finally. So all it took was dragon, some dwarves, elves, and a hobbit to get you two together?" McCoy shook his head.
"I guess." Kirk shrugged.

The next few days McCoy didn't see Jim or Spock but from what several crew members told him, the two of them were practically glued together. Where one of them was, the other one was within eyesight. It left McCoy wondering what really had happened on that planet after he himself had beamed back up. It was almost like both of them were afraid to let the other one out of sight.
After one week had passed, he finally saw the two of them in the mess hall and just couldn't help himself: "Spock! I see you finally found out you have feelings after all?"
"I do not understand the question," was all Spock said in reply, and turned to leave.
Before following Spock, Jim turned around and gave McCoy and apologetic look: "Sorry, Bones."
"No, you're not."