Leong Chee Mun, 37, pleaded guilty to an offence under the Covid-19 (Temporary Measures) Act.
Eleven people linked the case, including Leong's former fiancee Cassie Ong Shi Hong, 32, were dealt with in court last month.
Ong, who co-hosted the gathering, was sentenced to a fine of $4,000 on Aug 26.
Ten of their guests were handed fines on Aug 5.
Jackson Tan Chia Ho and Jasmin Tan Ee Lin, both 30, were each fined $3,000.
Poh Yang Ting, 21; Peh Si Qin, 22; Felisa Chua Jia Xuan, 23; Low Wei Hao, 25; Nicman Lim Wei Fong, 25; Chee Min Hui, 27; Kho Zi Ting, 27; and Priscilia Tan Sze Hui, 32, were each fined $2,500.
The cases involving six other guests are still pending.
During the circuit breaker period from April 7 to June 1, members of the public were not allowed to leave their place of residence without a valid reason or meet other people not living in the same place of residence for any social purpose.
Despite this, Jackson Tan and Jasmin Tan had been in Leong's flat at Block 295C Compassvale Crescent since around 6am on May 8 and had breakfast there.
The other guests later turned up from around 9pm that day.
While in the unit, the group mingled and came into close contact with one another while doing various activities such as eating, drinking alcoholic beverages, playing games and watching Netflix programmes.
A resident in the same block alerted the police to the gathering at around 2am the next day, stating: "This has been going on almost every night."
A police officer, Sergeant Roy Tan, later arrived at the unit and when he rang the doorbell, he heard "hushing" noises coming from inside. But no one opened the front door.
The policeman had to knock on the door, ring the doorbell numerous times and wait for about three minutes before Leong finally answered.
Leong told Sgt Tan that he was the owner of the unit, and that he had been sleeping.
He also lied to the officer, claiming that he and Ong were the only ones there, the court heard.
But the policeman called his bluff and replied that he had heard noises coming from inside the flat.
The court heard that Leong finally admitted that there was a gathering and police later found the guests inside the flat.
On Friday, Deputy Public Prosecutor Lee Wei Liang urged District Judge Brenda Tan to sentence Leong to a fine of $5,000, stressing that he had lied to a policeman.
Defence lawyer James Ch'ng, however, pleaded for a fine of $4,000. He said that the gathering was a private event and was not in full view of the public.
For each charge under the Covid-19 (Temporary Measures) Act, a first-time offender can be jailed for up to six months and fined up to $10,000.
A repeat offender can be jailed for up to a year and fined up to $20,000.