Earlier, 44-year-old King Mswati's 12th wife, 23-year-old Nothando Dube, also had to leave the royal household after she was allegedly caught in bed in August 2010 with Ndumiso Mamba, then Swazi Justice Minister who was sacked over the scandal.
Now, the King's sixth wife, Angela "LaGija" Dlamini, who has a nine-year-old child with her husband, has abandoned her palace, the 'Daily Mail' reported.
"She left the royal household last night, citing many years of emotional and physical abuse by her husband as the reason for her departure," the daily quoted a statement issued by pro-democracy group Swaziland Solidarity Network on Sunday.
The South Africa-based organisation, which campaigns for democracy in Swaziland, has quoteed an unnamed member of the royal family's security team who claimed Dlamini was now staying with relatives after fleeing her husband.
The statement continued: "A royal guard revealed that Angela had been unhappy for a long time and had actually thought of leaving her husband for many years.
"She finally packed her bags for good last night, initially pretending to be visiting her parental home in Hhohho.
From there she disappeared and is believed to be with relatives."
King Mswati's alleged marital troubles come amid continuing difficulties for the Monarch, who has been heavily criticised for his autocratic leadership of Swaziland which gained independence from Britain in 1968.
He is permitted to take multiple wives under Swazi customary law and traditionally selects a new bride each year during the country's annual Reed Dance festival.