Ford and Stan thought about allowing the kids to have their party, allow them to bask in their heroic victory over Bill Cipher, allow them to enjoy their innocence for just a little while longer.
Unfortunately, fate had other ideas. Dipper and Mabel came bounding in with huge grins on their faces.
"Hey, we noticed you guys left the party! Don't tell me you old men are tired already?" Dipper teased.
"I heard the phone ring! Was it Mom and Dad? They said in their last letter they would try to make it up here so we could spend our birthday with our whole family! Are they on their way?" Mabel asked excitedly. She noticed that Stan had tears in his eyes.
"Oh no, Grunkle Stan! Was it the IRS on the phone? Do we need to make the shack look like a church again to get us tax exempt? I can do my sad orphan girl schtick!" Mabel joked, having no idea of the cruel irony of that statement.
"Kids…it…it turns out you guys are going to be staying in Gravity Falls for a while longer," Ford said in a misguided attempt to soften the news.
"Wow, Grunkle Ford! You decided to take both me and Dipper in as apprentices?" Mabel said excitedly.
"Um…no, sweetheart," Ford said, unable to look her in the eyes.
"Oh, I get it! You're taking Dipper on, while I'm gonna learn how to be an awesome con man from this guy," she said putting her hand on Stan's shoulder.
Stan couldn't take it anymore. He had to get this over with. "Kids…your parents were on their way up here for your birthday…they were in a car accident."
The smiles quickly dropped from the kids' faces.
"Are they okay?" Mabel asked.
"No…your dad's in the hospital…it's…it's bad."
"What…what about Mom?" Dipper asked.
Stan bit his lip and teared up. "I'm sorry…she didn't make it."
Both the twins' eyes widened in shock. Dipper's face was emotionless, like his brain couldn't process what he was just told. Mabel, to the Grunkles' surprise, burst out into laughter.
"Oh wow, Grunkle Stan! You saved your best prank for last! And…and you're even crying too…I didn't know you were such good actors."
But as her uncles continued to cry, it finally dawned on her that this may not be a prank. "C'mon…this isn't funny. Where's Justin Kerprank? Come on...please...please stop…it can't be! It can't!" Mabel said, her voice growing in desperation and heartbreak with every word.
Dipper was crying, already accepting the truth. He knew his uncles wouldn't joke about something like that. Stan opened his arms and Dipper wept against Stan's chest. Neither cared about being "manly" at the moment.
"No! No! Dipper and I…we've gotta go home! Mom…Mom's waiting for us!" Mabel cried.
"Mabel…" Ford came over and bent down in front of her. He used his hand to cup her cheek. "She's gone, honey."
Mabel broke down tears. Ford tried to comfort her, but she pushed right past him into Stan's arms. Ford couldn't help but be hurt by this and was ashamed of himself for thinking such petty thoughts when his niece and nephew were suffering such a terrible loss.
Though Mabel was devasted about the death of her mother, she knew that she still had one surviving parent left. So in a shaky voice, she said, "I want to see Daddy."