Since its launch in 2016, This Is Us has been building towards resolution.

Tuesday's penultimate episode of the series was somehow one of the most emotional as Rebecca's (Mandy Moore) children said their last goodbyes to her.

At the top of the shocking installment, Rebecca's decline kicked off as her nurse ribbed lotion on her hands.

There was no response.

However, Rebecca's mind was still active, and we took a trip to the past as we got to see a much younger Rebecca.

The Pearson family matriarch was on a train, donning a beautiful red dress.

As a man approached, Rebecca declared she was waiting for someone.

But who was this mysterious man approaching our heroine?

William (Ron Cephas)!

What a throwback, huh?

If you watch This Is Us online, you know William was a big part of the earlier seasons of the series as Randall's (Sterling K. Brown) biological father.

Rebecca and William had a chat, and the former asked the latter to recite the poem that gave her the idea for Randall's name.

The plot thickened as William invited Rebecca to the bar on the beautiful train, but she remembers she was waiting for someone.

Rebecca decided to embark on the journey to the bar, and the rest of the episode jumped between this train ride and some shocking developments for the rest of the family.

We learned Rebecca's blood pressure was dropping and she was starting to slip away.

“Things are happening quickly now. I don’t see her making it through the night,” Nurse Laila declared.

Everyone at the house went in to say their last goodbyes to the woman who had a huge impact on their lives.

"Thank you for helping me with that complicated, incredible, beautiful boy that you raised. But I got him now," Beth (Susan Kelechi-Watson) shared as Rebecca heard it on the train through the speakers.

While Beth appeared on the train, William said the train was moving fast and that they had to get through everyone.

Dr. Katowski was revealed to be on the train, making drinks for everyone.

We told you this episode hit differently, you guys!

The only member of the Big Three not at Rebecca's side was Kate (Chrissy Metz), who was stuck on a tarmac in London.

The reason?

For work, and even though she didn't want to go, her brothers claimed their mother would not be impressed at letting such a big opportunity escape her.

Back on the train, Dr. Katowski told Rebecca there was a risk she would have died on the day the babies came into the world.

“You’re as tough as they come, Rebecca Pearson,” he shared.

“And you, my dear, have earned a rest.”  

When the train ride reached its final moments, Rebecca refused to proceed.

"I told you, I’m waiting for someone," she said.

We subsequently learned that Kate made it in time.

William opened a door that revealed a bed in it.

"This is quite sad, isn’t it? The end?” she wondered.

“The way I see it, if something makes you sad when it ends, it must have been pretty wonderful when it was happening,” he responded.

"The end is not sad, Rebecca. It’s just the start of the next incredibly beautiful thing. It’s like that dopey painting your son made that time," he added.

We return to the deathbed in the present, and Randall told his mother to "tell him 'Hey," clearly referring to their father.

She squeezed his hand.

We return to the train one last time as Rebecca lay on the bed. She turned to find Jack laying there next to her.

“Hey,” she said with a grin.

“Hey,” he responded.

Now, that's how you do a penultimate episode!

Just one episode of This Is Us remains, and it airs on May 24 at 9 p.m.