It's especially interesting in the wake of what looks like a fraudulent attempt to steal Graceland.

Riley won the legal battle a few days back when a judge halted the foreclosure sale, after Riley claimed her mom, Lisa Marie Presley never took out the alleged $3.8 million loan. The so-called lender then withdrew the claim. TMZ broke the story ... the FBI has been contacted and Tennessee officials are opening up a criminal investigation.

As for the birthday, the symbolism is key ... Riley and Priscilla have had a rocky relationship, especially in the wake of Lisa Marie's death, but they seem in lockstep now, at least in public.

The party seemed fun ... Riley was dancing up a storm and even tried a little remix at the DJ booth.

Pricilla's son, Navarone, posted ... "Happy Happy HAAAAPIEST of birthdays to the best mama in the whole world @priscillapresley, hope you enjoyed your night last night. I love you so so much thank you to everyone that came, and everyone that put everything together, and @chrisameruoso for the [photos],"