Rihanna and ASAP Rocky are celebrating their eldest son RZA's special day in the most “epic” way.

​The Diamond hitmaker and her longtime partner, who recently welcomed their first daughter together, their third baby, booked a slime-themed institute, named Sloomoo Institute, on May 13 to mark RZA's fourth birthday.

​The institute representative revealed that Rihanna and ASAP arranged custom slime-making stations and interactive installations for guests.

They also rented Sloomoo Institute's “Sloomoo Falls,” where the partygoers can drown in slime.

​The party also featured a "Mom-of-the-Year" moment, in which Rihanna got drenched in the slime fall with her kids.

​Clips posted in fan-based pages, Rihanna, along with her guest, can be seen singing the “Happy Birthday” song for RZA.

​Other videos also gave a glimpse of the birthday decorated with a fondant slime bucket and with the number "4" on it.

​Page Six revealed that an insider also reported that “over-the-top balloon decorations” were arranged at the bash.

​The source claimed that the family of five had the “most epic” time at their eldest son's birthday.

​It is pertinent to mention that Rihanna and ASAP Rocky are parents to three kids: sons RZA and Riot and daughter Rocki, who is only eight months old.