Disclaimer: Because this is still a thing? I guess? I own nothing of the rights to any of these characters/books/TV show, and some of the dialogue in this story is similar to some dialogue of the TV show.

I didn't actually research where characters were at this point in the show, so this could be completely off of what was happening behind the scenes in the TV show, but oh well, that's what fan fiction is for, right?

Alec/Magnus. One-shot.

What if Jace was lying to Magnus about knowing how far Alec and Magnus had gone in their relationship, just to save face? What really happened to Jace when all this was happening?

Jace and Izzy huddled over a screen in the middle of the institute, scanning for information on the latest greater demon terrorizing the city. The two of them were alone, spending a late night hunting while everyone else took a break. Clary was who knows where, and Alec was with Magnus, or at least that's what Jace thought anyway. He didn't ask any questions, but it was the assumption that Alec would be out with Magnus. Izzy had snuck Jace into the institute as well, because he was at the moment, not very welcome in this particular place, but she knew that Jace was an asset when it came to hunting demons, so she drug him over to help.

Izzy was staring intently pushing a few buttons to keep scrolling through the information, when Jace started getting a warm feeling in the pit of his stomach. His mouth started to form a grin, that he tried to prevent from happening, but it was automatic, pulling at the corners of his mouth. He gave a short laugh, and coughed.

Izzy looked up at him, questioning is judgement.

"What is it? This situation isn't something to laugh about, you know." She said, with a tone of irritation at Jace's inappropriate mood.

"It's not that, Izzy. Alec's in a good mood and it's transferring over to me, because of our parabatai rune." Jace replied back, still struggling not to smile insanely. Izzy rolled her eyes.

"Well, control yourself, because you are starting to look a little creepy." Jace nodded back at her.

"Yes, ma'm. Will not happen again." His mouth tightened, his body straightened, and he got himself into soldier mode as fast as he could, trying to make himself presentable.

They continued looking for a bit, Izzy commenting on possible locations that the greater demon may be found, when Jace all of a sudden felt an immense tingling in his groin, which caused him to turn beet red, and slightly dizzy. Izzy took that moment to turn and look right at him.

"What is going on?" She said as she glared at him. Her voice raised in annoyance that Jace could not keep it together.

"Ummm…I think Alec…is…uhhh…." Jace, a little breathless, looked to Izzy for help. It took her a few moments, but when she figured it out, her eyes widened in surprise.

"And now she's got it." Jace's sarcasm was dripping, but his voice still held a touch of air. Izzy squealed, spun around, and clapped her hands together below her chin.

"He took my advice!" She yelled, and Jace motioned her to keep it down.

"Sorry!" She whisper, screamed. "It's just so exciting. So can you really feel them having sex right now, because that is so awkward, but also fascinating." Her eyes sparkled in interest in this new found development.

"It's not exactly like that, Izzy, I'm just getting a sensation that started out as extreme happiness, then it turned into extreme arousal. Anyway, I'm happy for hi—" Jace cut himself off with an intense look that seemed to be the exact opposite of what he was just saying.

"Jace…what's wrong?" Izzy had a look of concern that mirrored the intensity of Jace's emotion, which looked more like fear, anxiety, and worry.

"I think something happened between the two. I'm not sure what just happened, but it feels like someone punched me in the gut. I'm now getting a sense of anxiety from Alec. So help me God, if Magnus did anything to hurt Alec, I am going to kick his ass." He was getting riled up, and started to pace back and forth near the screen that Izzy and him were standing next to. He started grumbling about all the things that he was going to do to Magnus when he got a chance. How dare that warlock hurt Alec? When Alec had put so much of himself on the line for this moment.

Izzy grabbed Jace's shoulder and turned him around, bringing him out of his anger.

"Hey, calm down, we still don't know what is happening exactly, you're only getting feelings from this, right?" "Yeah, but right now those feelings are so intense, and it happened suddenly like Magnus shut him down. It's such a strange feeling, how fast it happened, almost like—" Jace cut himself off again, and this time he grinned.

"Alright, false alarm, they're back on."

Izzy laughed, smiling back at him.

Jace, sitting on the patio of Magnus's apartment in Brooklyn, became irritated because there were cats all around him, distracting him from the work that needed to be done. When he could not handle it anymore he yelled for help from Magnus.

"Magnus!" The warlock in question walked through the patio door. Jace heard him talking to the cats, and explained to him why they were there, and how he could win them over.

"Well, when you put your mind to it I guess you can win over just about anyone, can't you?" Jace knew he sounded pissed off, but he wanted to be sure that Magnus had Alec's best interest at heart. He was still a little mad about the fact that Alec had anxiety during first time he ever had sex, and Jace's mouth decided to bring up this issue now.

Magnus figured out what his was talking about, and started to talk to Jace about his and Alec's relationship.

When Jace told him that he knew about the fact that they moved to the next level in their relationship, Jace realized his mistake and tried to quickly cover up the fact that he knew what was going on because he could "sense it". After seeing Magnus' face, there was no way in hell that Jace was ever going to admit to what he could feel the first time that Alec and Magnus had sex. It was just way too damn awkward.

A few days later, Jace and Alec were by themselves on Magnus's patio. It reminded Jace of the conversation that he had with Magnus, and he wanted to ask something of Alec, just to clear something up.

"Hey Alec?"

"Yes, Jace?"

"Do you…ummmm… ever know that I am…you know…" Alec eyeballed Jace with confusion.

"Do I know that you are ever what?"

"Do you know that I'm ever having sex?" Jace rushed, feeling his face burning a little bit. Damnit, he was never embarrassed about anything, why did he start now? Alec looked at Jace in surprise, but carefully said his answer back.

"Yeah…I do. But I never let it get to me. I figured that it was private, and that we didn't need to bring that up with each other." Jace nodded.

"Is it hard to control your feeling, though, when it's happening?" Jace asked.

"Nope, not really, why?" Jace groaned.

"Why do you have such good control over your emotions? It is so frustrating."

Alec began to laugh, understanding what Jace was saying.

"Did you feel when I had sex with Magnus, then? Is that what you are saying?" Alec was grinning, teasing Jace about his new confession.

"Yep, and Izzy was there, so she knows all about it, too." It was Alec's turn to go bright red.

"How many people know, Jace?" Alec asked, with wide eyes. Jace hurriedly replied.

"Just me and Izzy." Alec looked relieved.

"Okay, well as long as it's just the two of you who experienced one of the most private moments of my life…then I guess it's okay? You two are family, and you are parabatai, so I don't think I can be angry about the things that you in particular happen to know about me."

Jace nodded, and replied back.

"Agreed, as long as you keep those same moments about me to yourself."

"Agreed."