Lexie Grey is the daughter of Thatcher and Susan Grey (who passed away at the end of Season 3), and thus the younger half-sister of Meredith Grey. She also has a younger sister, Molly Grey Thompson.

Lexie is a graduate of Harvard Medical School.

At the end of Season 3 of Grey's Anatomy we learn that Lexie Grey will be a new intern at Seattle Grace. She was introduced in the penultimate episode of the third season as a woman Derek Shepherd met at the Emerald City Bar.

In the season finale, Derek confessed to Meredith that he met another woman (although he still doesn't specify who) and when she asks if she should be worried, he confirms her fears. While he didn't get together with Lexie, Derek admits meeting her was the highlight of his day.

Lexie Grey later made her first appearance in Seattle Grace when she introduced herself to George O'Malley, who was cleaning out his locker as she was on her way in. Upon hearing the name Lexie Grey, George clearly realized her connection to Meredith. What's to come of this new intern?

Lexie Grey Quotes

Lexie: The point is - I need to know what we are. What this is.
Alex: We're a thing, yeah we're together. We're a thing. Whatever.

That a hooker on your shoulder?

Lexie

Grey's Anatomy Quotes

There's a reason I said I'd be happy alone. It wasn't 'cause I thought I'd be happy alone. It was because I thought if I loved someone and then it fell apart, I might not make it. It's easier to be alone, because what if you learn that you need love and you don't have it? What if you like it and lean on it? What if you shape your life around it and then it falls apart? Can you even survive that kind of pain? Losing love is like organ damage. It's like dying. The only difference is death ends. This? It could go on forever.

Meredith

Arizona: Oh my God! I mean, I understand why you're into her. She's hot. Wait, she likes you?
Nathan: What? I mean, I'm going to try not to be offended at that.
Arizona: No, no, no. It's just that Derek was--Derek was epic for her. They were the great love story. I mean, that girl's heart beat for Derek Shepherd. It just...it never occurred to me that she would ever be with anyone else. He was perfect. He was everything. That man turned her world. It...I spooked you. Don't be spooked.