Grey's Anatomy Season 9 finale, "Perfect Storm," airs on Thursday night in the U.S. via ABC. Last week's episode promises a romantic development for Alex Karev and a very troubled phase for the fan favorite Calzona couple. To add to the drama, Jackson Avery has to come to terms with April Kepner's engagement to paramedics guy Matthew. And Meredith gives birth in a very difficult situation.

Spoiler Alert: This feature contains spoilers for those who have not seen Grey's Anatomy Season 9, Episode 23: "Readiness is All." Read at your own risk.

Grey’s Anatomy Season 9 Finale: Craniofacial specialist Lauren Boswell (Hilarie Burton from One Tree Hill/White Collar) is the new Mark Sloan? (CREDIT: ABC/Grey's/SpoilerTV)

Alex Karev and Jo Wilson are finally having a conversation that could lead to a kiss. But then a huge tree falls outside and pokes through Karev's window, splitting the two in a ruined romantic moment.

Wilson thanks Karev for caring. She has no idea the guy has just been seriously reprimanded for blackmailing. (There could be more on that later.) Karev, always emotionally stunted, tells her to "shut up." Avid Grey's Anatomy viewers knew it's time for the couple's first kiss. Well, that was the hope.

Grey's Anatomy Season 9 Finale: Shonda Rhimes Explains Cheating in the Calzona Story

Grey’s Anatomy Season 9 Finale: Craniofacial specialist Lauren Boswell (Hilarie Burton from One Tree Hill/White Collar) is the new Mark Sloan? (CREDIT: ABC/Grey's/SpoilerTV)

Craniofacial specialist Lauren Boswell (Hilarie Burton from One Tree Hill/White Collar) is the new Mark Sloan, apparently. And that's not just because she's great in plastics. Blame her for bringing the latest challenge in the just-recently-getting-better-relationship of Callie and Arizona.

"We've created this relationship that's very interesting and complex, and I feel like we're at a moment where this [temptation] feels earned. We're doing something that feels very in keeping with what's right for these characters," Grey's Anatomy series creator Shonda Rhimes told TV Line.

Rhimes explained the relevance of Hilarie Burton's character in the married life of Callie Torres and Arizona Robbins. The series creator brought up PTSD in relation to Arizona's character, hinting all the flirtation and the seemingly uncharacteristic cheating is part of a big picture.

Calzona fans should brace themselves. It seems a "heartbreaking" confrontation is coming. "That was the most stunning moment of the table read -- the entire cast gasped and fell silent," Rhimes told the Hollywood Reporter.

"I've done lot of reading on PTSD and grief and these people have been through a hell of a lot this season and we've watched them struggle to right themselves fairly quickly -- perhaps too quickly. There's stuff there that has not been dealt with. We're taking them through it, which I think is great, and Lauren is definitely possibly a part of that," Rhimes said.

Grey's Anatomy Season 9 finale will be filled with personal dramas among the characters as usual. The Calzona cheating is likely to deliver the biggest moment. But Jackson and Meredith have some big issues, too. Viewers should expect yet another mean serving of cruel cliffhangers.

Read More 'Grey's Anatomy Season 9 Finale' Articles:

Grey's Anatomy Season 9 Finale Part 1 Review: 'Out of Nowhere,' A Proposal, a Calzona Shocker, and the Wrath of Alex Karev! [READ]
Grey's Anatomy Season 9 Finale: Alex Karev, Jo Wilson Definitely Happening? What is Jackson Avery Doing? [READ]
Grey's Anatomy Season 9 Finale Spoilers, Clues: Fight for Life, Superstorm, Personal Drama, 'Monsters' [READ]