Mandy Moore Really Wants a Kate and Rebecca Duet, Plus 8 More 'This Is Us' Revelations

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Warning: Spoiler alert! Do not proceed if you haven't watched Tuesday's finale of This Is Us.

We still can't get over the season one finale of This Is Us!

ET joined the cast and crew of the beloved NBC series for a special finale event at the Directors Guild of America theatre complex in Los Angeles on Tuesday, where we learned some interesting behind-the-scenes secrets about the show, as well as a few season two teasers.

Now, we've rounded up all the best gotta-know-it facts from the Q&A session, all in one place.

WATCH: 'This Is Us' Finale: Jack and Rebecca's Marriage Suffers Its Biggest Hit -- Is it Over?

1. Milo Ventimiglia doesn't just play a dad onscreen.

The 39-year-old actor, who portrays patriarch Jack Pearson on the series, may not have any children of his own, but the cast and crew couldn't stop gushing over how great of a father-like figure he is on set.

Susan Kelechi Watson (Beth Pearson) said she even has a nickname for him: "Spoiler alert. It's papa bear," she explained. "Because Milo takes care of us, man. He's just so caring."

Mandy Moore (Rebecca Pearson) chimed in, telling the crowd, "I thought I was a nice person until I met Milo. I did. I was like, 'I feel like I treat people well.'"

"It is an easy and enjoyable thing to be good and look out for the people I know are looking out for one another, and looking out for me, and the process of making a great show that everybody can enjoy," added Ventimiglia. "I come to work with a full tank specifically for this group."

"It's fun," he continued. "I feel like we have as a group, in 18 episodes and 17 months of filming, managed to stay connected, even in the moments when we're not working there with one another."

2. Justin Hartley was just as impressed as fans by Moore and Ventimiglia's fight scene in the finale…

Fans have seen Rebecca and Jack get in a few minor tiffs throughout the first season, but none were as serious as what happened between the two Tuesday night, which ultimately led them to separate -- for now, that is.

"One of the best things about being on this show is being part of an ensemble," Hartley, who portrays Kevin Pearson, gushed. "[I] can watch parts of this show that I'm a huge fan of, that [I'm] not in, and watch it as a fan. And watching [Mandy and Milo] work together was some of the best acting I've ever seen in my entire life and I'm kind of a TV junkie. I watch a lot of TV, and that's some of the best acting I've ever seen in my whole damn life."

According to Ventimiglia, fans will receive some answers on the fate of Jack and Rebecca's relationship next season. "It will all come together as it's supposed to," he teased.

3. …but admits he didn't think he was "good enough" to act out the emotional scene with Randall during the "Memphis" episode.

Although Hartley had no problem praising his onscreen mom and dad for their acting skills, he confessed that while reading the script for episode 16 -- in which he has a "What would Jack do?" moment and leaves his play opening night to check on Randall, portrayed by Sterling K. Brown -- he had doubts.

"One of the things about being an actor is, sometimes you'll read things and be like, 'How am I gonna save this? It's horrifying?'" he explained. "But almost more horrifying is when you read something and you're like, 'This is so [good], I don't think I'm good enough for this.' And that's what [my co-stars] all do. Somehow it all works out."

"Justin, you step up to the plate and you deliver!" added Ventimiglia.

4. Jack and Rebecca were supposed to be matched up with each other on their blind dates, but the writers changed the story last minute.

Surprise! While watching the finale Tuesday night, fans assumed that the girl Mrs. Peabody was trying to set Jack up with was Rebecca the entire time. Issac Aptaker and Elizabeth Berger, who wrote the finale with writer Dan Fogelman and have been named co-showrunners for the second season, "didn't quite feel right" about that scene, however.

"At the very, very last minute, I think the 11th hour, we came up with this notion that you think they're going to get set up with each other by Mrs. Peabody, [then they don't]," Aptaker explained. "That was literally in the office at 1 a.m."

5. Chrissy Metz wants her character, Kate Pearson, to get married, but isn't ready to say "I do" in real life… yet!

She has a boyfriend both on- and off-screen, but Metz, who is dating This Is Us cameraman Josh Stancil, revealed she and Kate are on total different paths when it comes to tying the knot.

"Girl, no. Pump the brakes! One day at a time," she joked about a possible engagement to Stancil. "But Toby [Damon] and Kate? I don't know. You might be hearing wedding bells. I mean, I want a dress. I want a cute wedding."

Her onscreen beau, Chris Sullivan, weighed in, saying, "[The writers have] given us a great relationship to be a part of. If only you had TV writers writing your relationship!"

But don't expect Toby and Kate to be all lovey-dovey on season two. "I think they're coming down from the dopamine serotonin festival of falling in love," he teased. "And now I think it's about to get real."

6. Mandy Moore is so down for a Kate and Rebecca duet!

"I wanna hear Chrissy sing," she dished. "I mean, maybe a Kate and Mom duet [next season]?"

And Metz is definitely on board with that idea. She said she's extremely excited about singing more next season -- the writers teased there will be "a lot of singing" because the 36-year-old actress has "a beautiful voice" -- especially because she was once told to basically give up her hobby.

"My first-ever manager was like, 'Maybe you shouldn't do the singing,' so I kinda put that in the back of my mind," she revealed. "So it's kinda fun. I get to explore this like, 'All my dreams are coming true!'"

7. Susan Watson teases what's to come of Randall's desire to adopt.

Another major moment during the finale was when Randall told Rebecca he would love to expand their family. According to Watson, the decision may not go down as easily as expected.

"I think the adoption thing could be an issue, I think, because even earlier in the season when [Beth and Randall] had the pregnancy scare, she was sort of looking forward to a time in her life where she could do other things and not split her time between being at home and raising the kids and trying to jumpstart a career," she said. "It's a huge undertaking to take on an [adopted] child, as we've seen from Jack and Rebecca, the challenges of that. So,you know, it's a tough time in his life. This [turning] 36 thing has totally thrown him into some other place, but she wants to be there for him. At some point I think she really wants to figure some things out for herself."

Ron Cephas Jones, who portrayed Randall's birth father, William, has his own theory. "[Beth] may go into the workforce, and Randall may have to stay home. Could be!"

8. Chris Sullivan has another name for the series.

With all the fan theories on how Jack died, Sullivan joked that This Is Us is like "that Neil Patrick Harris show," How I Met Your Mother.

"If we stretch out the reveal for like seven seasons, it would be called How I Killed Your Father," he said.

9. Everyone still is on the fence about Miguel.

When asked about the craziest fan theories they've heard about Jack's death, Ventimiglia referenced the murder-mystery game Clue. "Craziest fan theory is Colonel Miguel in the library with a hammer," he joked, as Sullivan quickly reminded the crowd that "Nobody likes Miguel."

"I don't NOT like Miguel," added Hartley.

Looks like Moore is the only one who has his back. After all, Rebecca does end up with him once Jack is out of the picture.

"Save Miguel!" she exclaimed.

WATCH: Milo Ventimiglia and Mandy Moore on'This Is Us' Finale: Jack and Rebecca 'Needed a Break'

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