Heidi and Spencer ahhhhh Hverjum er ekki .......

So now we know why Heidi and Spencer went to the Bev Hills Courthouse on Wednesday. They said they didn't get a marriage license - pants on fire.

We've learned that's exactly what they did. It's under seal, but it's real. And they're getting hitched on Saturday.

All invited guests will receive 10 copies of Heidi's latest single ... this part we're guessing, but it's a safe bet.

Source: TMZ