On Friday, Walsh posted a clip of her first scene on the ABC medical drama. In the video, Walsh's character, Dr. Addison Montgomery, goes up to her estranged husband, Derek Shepherd's (Patrick Dempsey), as he's talking to his current lady love, Meredith Grey (Pompeo).
"Unreal that today marks 15 years ago to the day since this little lady walked on to your screen and checked ya for screwing her husband," Walsh wrote alongside the clip on her social media.
Pompeo retweeted Walsh's post, adding, "@katewalsh thank god I messed with your hubby!! ?? ? it worked out well for us both!!! Love you so much and THAT scene ...when your character showed up ...was such a defining moment for this show. From that point on we had them hooked!!!"
Dempsey also chimed in on Walsh's Instagram, adding three hand clapping emojis.
Walsh was on Grey's from 2005 to 2007 before she starred in her own spin-off series, Private Practice. She would return to Grey's as a guest character. Dempsey would go on to depart the drama in 2015 after 11 seasons.
Pompeo, on her end, continues to lead the Shonda Rhimes series, which got renewed for seasons 16 and 17. In 2018, Pompeo addressed the future of Grey's and was candid about when she'd hang up her scrubs as Meredith.
"It's something Shonda and I will decide together," Pompeo told ET. "I've been doing it a long time and I do get restless, but the fans are just still so passionate about the show."
"I think the fans will let us know," she added. "When the numbers start to drop and people aren't watching the same, people aren't as passionate about it... it's time to call it."