A true bridesmaid is by your side on the wedding day and, if needed, post-divorce.
Lambert sang and swayed along to Monroe's performance, later joining her BFF on-stage for a live duet of her hit "Heart Like Mine," which she co-wrote with Monroe.
Monroe is hardly new to the country scene. In fact, together with Lambert, the pair make up two-thirds of the country girl group The Pistol Annies. (Angaleena Presley -- with whom Monroe and Lambert once co-starred on an episode of Say Yes to the Dress -- rounds out the trio.)
Monroe's third studio album, The Blade, will be released on Friday, but country radio listeners are likely still hearing her voice on Shelton's recent hit, "Lonely Tonight." In fact, it was Shelton that officiated Monroe's own 2013 wedding to White Sox pitcher John Danks. (Lambert, of course, served as maid of honor.)
Pop music fan? Perhaps you know her from Train's 2012 single "Bruises." Last summer, singer Pat Monahan told ETonline: "I wanna reconnect with Ashley and take advantage of her coolness." Adding with a laugh, "I don’t know if that means we'll make a record together someday, or what that means, but any time I get to be around Ashley is a great time for me."
Lambert herself sang Monroe's praises in an interview with ET at this year's ACM Awards, where her then-husband, Shelton, served as host and Monroe as her date.
"She's a great country singer and she's inspiring to me," Lambert said of her pal. Later, the "Smokin' and Drinkin'" singer would win three trophies
including album of her year for Platinum
"I'm just beaming, I tell you what," Monroe told ET. "I just look up to her so much. I've known her for 10 years and we've been best friends for almost 10 years, but I still watch her shows every night when I'm on tour with her and anytime I'm out on the road just hangin' out, I just watch her because she just blows me away. She's the real deal, for sure."
With Monroe's latest album in the can, fans may be able to look forward to new music from The Pistol Annies.
"Angaleena just released a record and Ashley is about to release another solo record and I'm working on another solo, so we’ve been texting a lot and just trying to figure [everything] out," Lambert told ET. "When we get in a room it's magic and so we just have to find time in our schedules… to just get in a room for a couple of days and I'm sure more magic will happen."
As for her own Platinum follow-up, we'd venture to guess there will be more than a few breakup anthems this time around. But if Lambert's past work is any indication, we're gonna love it.