'When my ex took our daughters to meet his new girlfriend, I knew I had to say something.'

Erica Keane had been married to her husband for 15 years when they separated abruptly. He soon moved on with a new girlfriend — but sharing two kids, Erica was determined to find a way to navigate the new family dynamic, if only for the sake of her daughters.

But blended families aren't always easy, especially when it comes to co-parenting and sharing time between old and new partners. And when Erica's ex told her he wanted their daughters to meet his new partner, she decided to take action.

Watch: Co-parenting advice from an expert. Post continues after video.

Having never met her ex's new partner, Erica came up with a plan to share an open letter to the new woman in his — and by extension, her children's — life.

The letter, which Erica read out loud on TikTok, began: "I haven't met you yet, but today's the first day that you're going to meet my girls, my daughters.

"I want to say thank you first of all for opening your home to them and being willing to give them a place to stay so they could spend time with their dad."

Erica expressed her gratitude to the new girlfriend for being "willing to facilitate a relationship" with the children, as let's face it, this isn't always guaranteed in blended families.

"I just want you to know that I'm here," she continued. "You don't know a lot about me, or maybe you do, but I don't really know you at all, and I'm happy to talk anytime you're ready."

Confessing that this family dynamic was new her, Erica shared that she wanted to use TikTok as a platform to reach the girlfriend, and offer some information about her daughters.

She explained that Avery, her youngest, loves American Girl dolls.

"She said she can't wait to show you," Erica said of her nine-year-old. "She also loves to do her skincare. So she brought all of her skincare stuff. I know it's overkill. When you see it, you'll think, 'she doesn't need all this.' One hundred per cent she doesn't."

The mum also warned that her youngest is a picky eater and packed "really awful plaid leggings".

"You can get rid of them, hide them… you have my permission," Erica said, concluding by saying Avery is "really precious" and "fun".

Erica then described her eldest, 14-year-old Kaitlin, as "real smart" and "wise".

"She loves music. She wants to share her playlist with everybody. Actually, that's not true. She will gatekeep that playlist. It's her special, prized possession. But she does love music," Erica said.

"She loves art. She has a lot of friends that she keeps in touch with on her phone, so she's constantly texting," she added, suggesting the new parental figure could take the phone away if the teen became too glued to the screen.

"She's a lot of fun whatever she does, but she does have that teenage attitude. So if you need anything on that, let me know."

Erica said she was excited to hear about the weekend and the "memories" her kids make with her ex-husband and his new partner.

"It's all new to them, too. They've been through a lot this year. They're kids. They're resilient. But I'm really proud of them for how they've taken all of this. This is one more new thing for them," she said.

"Not a lot of kids can say that they have extra people in their lives to be excited for them… I'm thankful for you for being another person in their life, to see how awesome they are and to love them."

The Oklahoma local also explained it was important to her that the women communicate, mother to mother, with the father, so the three of them are able to make decisions with the children's best interests at heart.

"Going forward is my most favourite thing, because we get to sort of recreate and start fresh," Erica mused. "I'm thankful for that chance, and I'm thankful to see their dad grow and be the best dad that he can be through otherwise really hard situation.

"They deserve that, so thanks for making him happy and giving him that opportunity to be the dad that they really need."

Erica finished by reiterating how much she wanted to meet the new partner, so they could "learn about each other".

"No one says we have to be besties, but we're we're intertwined now more than ever, for a long time. So, welcome to my life. Welcome to the best part of my life, those little girls. Have fun with them. Love on them. They're amazing," she said.

The mother-of-two was quickly inundated with support.

"The death of our ego is the absolute birth of unconditional love. God will reward you greatly. ❤️❤️❤️," read one comment.

"I must say, if there was an award for mother of the year, girl, you would win hands up how," a second penned.

"Wow… as a stepmum I'm seriously moved by this! If only every co-parenting situation could be this way. So much respect for you as a mother ❤️," a third added.

"This made me cry. Thank you for reminding me there are wonderful mums just like you out there that want to build positive relationships with stepmums because you love your kids that much. ❤️," read one more.

And after Erica picked up her kids at the end of the weekend, she shared a much-anticipated update.

"My girls said they had a really good weekend and we are just really happy to be home," she shared.

After the video went viral, racking up 2 million views (and counting), Erica told PEOPLE magazine that it was her mother and stepmother's relationship that inspired her to make the TikTok.

"[My mum] never, ever thanked my stepmum. And in that moment, I said, 'Okay, start to spin your thoughts a little bit,'" she said.

She also confessed that she wanted the new girlfriend to "see her character" through the phone.

"I wanted her to know that I do not hold animosity or grudges, and I'm good," Erica said.

"But really, truly, if it comes down to it, I probably made it out of the fact that I felt so misunderstood."