Sam was worried for his brother. Dean hadn't been acting right for days, not since Castiel had flown off to attend to whatever kind of angel business he had to take care of. The older hunter had been bitching about pain stemming from his chest and radiating throughout his body for days. He had also been moody, and despite claims of feeling nauseous, he had been eating non-stop. At about the two week mark of Cas' absence, Dean began complaining of violent pains in his shoulder.
"The shoulder where your angel hickey is, right Dean?" Sam asked, a knowing tone in his voice.
"Shut up Samantha." Dean grunted back, his voice obviously attempting to hide the pain.
"Seriously though, that's the one, right?" Sam tried to sound sincere, and apparently it worked, as Dean actually gave him an (albeit curt) answer.
"Yes Sam. That one."
Sam decided he would suggest the cause to his brother's pain to him, but he knew that Dean wouldn't like it, hell, he probably wouldn't even admit to it. See, Sam had done some angel research, (behind Dean's back of course) by himself and with the newly not-dead archangel Gabriel. What he had gleaned from these research sessions was that A: Dean and Castiel were an item (Long story short, Gabe can go invisible and see and relay things to Sam that have him reaching for the brain bleach) B: Dean did not plan on telling him this at any time in the near future, and C: Long periods (meaning more than a day or two) of the separation of an angel from it's human mate caused discomfort and even pain for both. This meant that Cas had to be feeling it as well, which caused the younger Winchester to be puzzled as to why the angel had not returned. This wouldn't last long however, because at that moment, Castiel appeared in the bunker's library.
That was also about the moment when Dean passed out.
Dean awoke on his bed, and the first thing he registered was that the pain was gone. He then noticed Castiel, whose hand was in his own.
"Cas?" Dean asked, "Where have you been?"
"Dean. I am so sorry I was away for so long. Heaven is in utter chaos, and I was needed for longer than I anticipated. Please forgi-" Cas was cut off as Dean pulled him into a kiss.
"AHA!" Sam said, bounding through the open door. "I knew you guys were together! Fucking fin-all-y. Gabe, you get in here too!" Sam called out over his shoulder. The lively archangel strode through the door, took one look at Dean's shell-shocked face, and began to laugh.
"Deano, you weren't hiding your 'thing' with Cassie over here nearly as well as you thought you were. In fact, you were so un-subtle that we all had a betting pool on when you'd finally bid adieu to Narnia and join the rest of us outside of the closet."
"Wait, wait, wait" Dean said, and incredulous look twisting his features, "you all? Who the hell is you all?"
It was then that Cas decided to speak. "Dean, I believe the pool included Sam, Gabriel, Charlie, Kevin's ghost, Gadreel, Abbadon, Samandriel, Crowley, Linda Tran, Jody, Juliet the hellhound, Meg, Naomi, Cain, Jo and Ellen, and Benny, along with a few others. Obviously some will not be able to collect, however."
Dean just sat there, stunned. And he thought he'd hid it so well. Even a damn hellhound was in on the action? Really? The worst part was, that wasn't the weirdest thing he'd ever heard.
"Well," Dean began, "did Juliet win?"
The four men laughed, but when Dean asked for food, the others looked at one another, and became somber. This was something Dean was used to, and it rarely meant anything good.
"Fear not," Gabriel began in a theatrical voice, "for I bring you tidings of great joy."
The elder Winchester was confused, and it showed on his face, which caused Gabriel to decide that Dean needed to be brushed up on his Bible knowledge, but not until more important matters were attended to.
"Alright Deanbo, I'll dumb it down for you. There's gonna be a angel human baby born. It's gonna come outta you. Castiel the stud muffin over here is you angel baby daddy." That was what Gabriel said, but Dean kind of stopped listening after 'it's gonna come outta you'.
"WHAT?" Dean exclaimed. When he saw Castiel's sheepish look, he muttered, "Cas. Did you know this would happen?"
"Well, no Dean. I knew it was a possibility; however, I didn't think it would happen. I thought that the mating statutes weren't completed, and therefore there would be no nephilim."
"We're just gonna see ourselves out." Sam said, half-dragging the nosy Gabriel from the room.
"Explain." Dean said.
So apparently, when an daddy angel and a mommy human love each other very much, and angelic dibs (Dean's term, Cas used a very fancy Enochian word that Dean couldn't hope to pronouce) is invoked, and the two in question 'copulate' (classified as a physical expression of that love), the angel's grace can reach out to the human's soul and the two intertwine, creating an all new being. Cas explained to Dean that his handprint, along with the inscription on the hunter's ribs, bound Dean to him, and essentially showed to all Creation that Dean belonged to the angel Castiel. The reason Dean had been experiencing pain in Castiel's absence was because after they 'expressed their love physically', in the eyes of the Heavenly Host and God himself Dean was officially Castiel's mate. The moodiness and nausea were stemming from the nephilm. The baby was made of something else Dean couldn't pronounce at this point, but after it detached itself from Dean's soul in four to five months it would create its own vessel, which would contain traits from both Dean and Castiel's vessel.
"Wow." Dean said
"I know." Castiel agreed.
Dean was excited. He'd get to be a father, to his child with the love of his life, which was something he hadn't even let himself dream about. Now the only thing was explaining this all to Sam without setting himself up for 'mommy' jokes for the rest of his life.
Sam already knew thanks to Gabe, he had learned at this point to just accept it, and was planning the mommy jokes already.