Izzy walked in to the kitchen to get herself some tea, but stopped when she realized Jace was already there sitting at the table. His eyes were wide and his expression pale as if he'd seen a ghost.

Izzy took a mug from the shelf and tried to pull him from his reverie.

"Jace? You okay?"

The blonde nodded, not tearing his eyes off the table top, unusually silent. It was well past midnight so Isabelle figured he was just tired, and kept talking; unfazed by his lack of interest.

"So, the downworlder meetings seemed to go well, despite the Luke trying to kill Valentine thing. I was thinking of making a cake to celebrate Alec's first victory as Head of the Institute. What do you think? Maybe I should ask Magnus to help, I think he's still here. I'll go find him and-"

Jace's face suddenly snapped towards her, looking panicked.

"No! Don't do that!" His voice was a little too loud for the quiet kitchen and Izzy made a face at him.

"If you're trying to tell me I can't make a good cake, you can save it because Raphael taught me this really great recipe with-"

Jace shook his head and rolled his mug of tea between his palms.

"No, it's not that. Well, actually you should probably let someone else handle the baking. But I meant you shouldn't go talk to Magnus he's … busy right now."

The shadowhunter looked a little sick as he shuddered. Izzy sat down beside him, abandoning her own mug.

"What are you talking about? And why do you look like you're about to throw up?"

Jace leant towards her, keeping his voice low as if sharing a secret.

"Did you know Alec has a birthmark on his ass? I didn't. Now I do."

Izzy let out a little laugh, scrunching her nose up adorably. "So you walked in on Alec getting changed?"

Jace shook his head, eyes begging Izzy to understand what he was silently saying so that he wouldn't have to speak the words out loud.

She suddenly got what he was meaning and burst into laughter.

"Oh, by the angel, that's funny."

Jace looked upset as he scolded her. "It's not funny! They were doing things that I never wanted to see our brother do."

"It's nothing you haven't done before, I'm sure."

He shook his head again, pouting unhappily. "Nope, never done that."

Izzy was still laughing. Wiping at her eyes with a careful finger as she watched Jace's face.

"Why did you go in there?"

The blonde threw his hands up, exasperated that he wasn't being given any sympathy.

"I didn't know what they were doing! I heard Magnus call each Alec "Mr Lightwood" and thought they were still having the downworlder meeting or something. But, in his bedroom for some reason? Then Magus made a very gross joke about Alec being head of the institute."

Izzy burst out laughing again, clutching her stomach as tears ran down her cheeks.

"Oh my god, I can't believe you walked in on them!"

Jace shuddered again, and frowned grumpily at Izzy's reaction. "I'm glad you think it's funny, because I won't be able to look either of them in the eye, ever again. I'm scarred for life."

*Meanwhile, in Alec's bedroom*

"Do you think maybe you could erase Jace's memory of this?"

Magnus smiled and ran his hands appreciatively down Alec's chest, watching as his painted fingers bounced over those abs.

"I'll do it tomorrow. Right now, we have other matters to attend to. You have the High Warlock of Brooklyn sitting in your lap, and he need's your undivided attention."

Alec hummed in agreement and gripped Magnus' waist where the man straddled him.

"Hmm, whatever you say Mr Bane."

Magnus leant down and kissed at the rune on his loves neck, letting Alec feel the soft bite of his teeth. He could feel Alec's heart beating rapidly beneath his palm, and spoke with his lips still pressed to his skin.

"Are you mine, Mr Lightwood?"

The Nephilim could barely form a sentence, only managing to get out a moan and a single, gasped word.

"Always."