Inkhosikati LaDube, who is now 23 and married King Mswati III at the age of 16, claims she has been kept under virtual house arrest in her official residence since she and Ndumiso Mamba were caught in a hotel in Swaziland's capital Mbabane.
She told a South African newspaper that after over a year in captivity, she was ordered "immediately to leave the palace" on November 12.
It followed a row with a security guard who blocked her from taking the youngest of her three children, a two-year-old, to hospital after he injured himself playing, she said.
"He threatened to hit me, saying I am not going anywhere with my child, who was bleeding from a deep wound," she said.
An altercation ensued, she told South Africa's Sunday Times, and she was "physically prevented" from leaving the palace. "I had to protect myself so I pepper-sprayed him in the eyes."
The matter was reported to the Queen Mother, who shares power with her son and is known as the Indlovukazi, or Great She-Elephant. She is said to have decided that LaDube had been disrespectful and should be evicted from the Royal household.
LaDube said she was forced to leave behind her children and her belongings.
"They just said 'you have to pack and leave now'," she said.
The King, who is 43 and has a total of 23 children by 13 wives, is currently on his annual period of seclusion. He has not seen LaDube for nearly a year and, she alleges, knows almost nothing about the couple's children.
Swaziland Solidarity Network, a South-Africa based umbrella organisation of Swazi pro-democracy NGOs, lambasted the king for LaDube's "brutal eviction".
"The ill-treatment that LaDube has endured and the subsequent separation from her children is a very inhumane act," spokesman Lucky Lukhele said.
He said the king had "never forgiven" LaDube for embarrassing him with her alleged affair.
"Since then, LaDube has endured a terrible existence at the hands of the Swazi royal family," Mr Lukhele said.
"Mswati has never again set foot in her house after the scandal. He further instructed her bodyguards to deliberately frustrate her to the point where she could no longer take it and then hopefully leave."
He added that without their mother, LaDube's children were at risk of being "terribly neglected" in the Royal household.
King Mswati, who was educated at Sherborne School in Dorset and was an invited guest at the Duke and Duchess of Cambridge's wedding earlier this year, is Africa's last absolute monarch.
His personal wealth is estimated at between $100m and $200m, while the lion's share of Swaziland's 1.4m people live below the poverty line.
Swaziland is currently in dire financial straits and unable to pay civil servants, but King Mswati has stalled on a bail-out from South Africa because of the democratic reform conditions attached.
Last week, it was reported that the tiny southern African kingdom has failed to pay more than $10m (£6.3m) in grants to Aids orphans. More than 25 per cent of Swaziland's adult population is infected with HIV/Aids, and tens of thousands of children are orphans as a result.
Orignal From: Twelfth wife of Swaziland kicked out of palace over affair with justice minister