The Avengers, and Maria because she got there early, were casually having breakfast, talking amongst themselves, when Tony Stark noticed something. Natasha and Maria were sitting close to each other, a little too close. There was plenty of space around the table, they could easily just split apart. But they don't, why?
That's when it hit him, the lingering touches, the longing looks, it was right in front of him;
"Romanoff, are you dating my sister?"
Heads turned towards him, "Your what now?" Steve asked, a little confused.
"My sister."
"Maria's your sister?!" Natasha stared at him with wide eyes.
"Unfortunately." Maria sighed.
"You and Stark are related?!" Natasha continued her rant, "And you didn't even tell me?!"
"I was planning on telling you later but it seems he cut me to the chase." Maria glared at him.
"So you two are really related?" Bruce asked, looking between them.
Tony shrugged. "Pops had an affair and I was stuck with babysitting duty for years."
"Don't pretend like I didn't babysit you back." Maria rolled her eyes.
A few more questions came along, about their childhood, and what it was like growing up with the Tony Stark.
Tony adored Maria, he still does but they don't need to know that, which made him very protective of her. She gets sick? He cancels all of his plans and takes care of her. Boys taking interest in her? He made sure they stayed away from her. When Maria came out as a lesbian? He gave her a whole speech about how much he accepts her. He also said; "We can talk about girls together!"
When Maria told him that she wanted to become a soldier, he cried, just a little bit. Maria was smart enough to get into any college she wanted to. They were already talking about which university she should go to, but as the supportive older brother he was, he just cried because he won't be able to see her as much anymore. He also won't be able to protect her. He couldn't talk to anyone to make her job safer because people would wonder why the young billionaire would want a specific Marine to be given special treatment. So he just kept hoping that she won't get hurt too bad or die. He'd probably lose his shit if he loses Maria.
Clint turned to Tony, "Is that why you threw that one dude off the Helicarrier because he was hitting on Maria?"
"Wait, you saw that?" He was on his annual visit to SHIELD when he noticed an agent looking at Maria with heart eyes, he let it go since everyone looks at her that way. The man actually approached Maria, who rejected him obviously, but he kept on forcing her to go out with him. Tony dragged him to one of the far corners of the Helicarrier, said "Should've taken no for an answer, buddy," attached one of his boots to the agent's pants and threw him off to who knows where. He then transfered him to another base.
"I wouldn't be asking if I didn't."
"Is that what happened to Agent Jones?" Maria asked, Natasha looked at her questioningly, "He asked me out on a date once and I never saw him again."
Everyone looked at Tony again.
"Oh don't be so dramatic. He's alive." He rolled his eyes, "I attached one of my boots onto him and threw him off the deck. After that, I had him transferred to another base."
"Bit overprotective, are you Stark?" Steve teased him.
"Well in my defense, he looked shady."
Maria raised an eyebrow, "Really? That's your reasoning?"
He just shrugged. "Back to the more important question, are you two really dating? As her older brother, I think I have the right to know."
"Yes, we have been, for 2 years now."
"Did you guys know about this?" He pointed at the others.
All of them nodded. "They never really tried to hide it." Bruce shrugged. "I'm actually surprised that you didn't know."
Tony gasped dramatically, "Jarvis, play Traitor by Olivia Rodrigo."
Natasha chuckled, "Damn, you Starks are oblivious." She smirked, "Is it a family trait or something?"
Maria just rolled her eyes.