This Is Us
This Is Us stars Mandy Moore as Rebecca and Milo Ventimiglia as Jack in the lead roles NBC

NBC drama This Is Us has left fans teary-eyed with almost every episode aired so far. After the winter break, the show returned with some back-story into the emotional past of the Big Three and one question that looms ahead is about the heartbreaking death of a beloved character – Jack Pearson.

For the first time, This Is Us gave a glimpse of Milo Ventimiglia past when it aired Jack's funeral ceremony in episode 12 titled The Big Day. One of the first flashback episodes of the season revolved around the romantic life of Jack and Rebecca before the birth of their triplets.

Click here to watch This Is Watch season 1 episodes live online on the official website of NBC in case you missed it on TV.

While Jack's unfortunate death is no news to the fans, there's still some suspense surrounding the events that led to the demise. What eventually led to Rebecca marrying her husband's best friend Miguel and how did the children grow apart? As it turns out, fan theories have some crazy answers to all these questions.

According to one Twitter user, Ventimiglia's character's death is closely connected to his on-screen daughter Kate and Toby's storyline. When Kate realized that her on and off boyfriend was reluctant to get surgery for his heart condition, she was paranoid hinting that her fears might have roots in her past.

Did Jack die of a heart-attack?

"Kate's reaction over Doofus being a scaredy-cat about the surgery makes me wonder if Jack's death was heart related?" teased the fan.

Jack's death has also been connected to the tragic 9/11 attack in another fan theory that was recently posted to Tumblr. Shared by an user named just-an-outlaw, the theory draws parallels with the scenes where Jack and Rebecca's three children are scared while aboard a plane.

The best of all theories – and also the one which every This Is us fan is hoping to be true – is the one, which predicts that somehow the NBC show creators would reveal that Jack is alive. "So, they faked Jack's death... the urn is just filled with ashes from the fireplace... He's going to magically reappear. #alternate#thisisus," a fan shared on Twitter.

If that turns out to be true, it would be even more heartbreaking to explain why Rebecca – played by Mandy Moore – went on to marry Miguel (Jon Huertas) in the end.

Watch This Is Us on NBC on Tuesdays to find out the truth behind Jack's death.