"After a long meeting [on Monday] to discuss the DA's values and the DA's constitution, I can confirm that AbaThembu King Buyelekhaya Dalindyebo has joined the DA," Athol Trollip said on Monday.
Trollip said earlier on Monday he was meeting the king near Mthatha.
Last month, Dalindyebo made headlines when he reportedly described the ANC and President Jacob Zuma as "corrupt hooligans". He made the remarks in Qunu, in the Eastern Cape, at a prayer service for ailing former president Nelson Mandela.
Dalindyebo reportedly said the ANC had distorted the anti-apartheid icon's legacy and behaved arrogantly. He said he would stop smoking dagga the day Zuma stopped being corrupt.
Dalindyebo also said he would join the Democratic Alliance as a birthday gift to Mandela. Mandela, who remains in a critical but stable condition in a Pretoria hospital, turns 95 on Thursday.
On Saturday, AbaThembu royal family spokesperson Nkosi Daludumo Mtirara said the family had apologised to Zuma.
He said at the time that a resolution in September last year, to remove Dalindyebo as king, had not been finalised.
"I'm simply going to go and see him about signing up his own personal membership."
Trollip said Dalindyebo had contacted DA leader Helen Zille and himself on a number of occasions since 2010 saying he would like to join the party.
"So when he made a widely publicised statement that he'd become disillusioned with the ANC and wanted to invite Helen and me to come and talk to him about joining the DA, and about what role he could play in helping the DA establish itself in his area of jurisdiction, obviously we had to respond to that."
On Wednesday, Dalindyebo said Zuma dealt mercilessly with perceived opponents after he handed a petition to officials of Zuma's office at the Union Buildings in Pretoria.
"He flushes people like condoms. Like yesterday [July 9]. He thinks he can flush kings, he flushes his ministers like condoms," he said.
"Unfortunately, the president has a habit of not condomising. We don't like people with that kind of attitude. His behaviour is a shower mentality."
'He's just a Zulu boy'
Zuma announced a Cabinet reshuffle on Tuesday.
Dalindyebo said he expected a "practical response" from Zuma to his petition.
"He must tell AbaThembu about his intentions and AbaThembu need to direct him to the rightful place. I cannot be ordered to his office. He must come [to] my office," he said.
"I am king unto him, he's just a Zulu boy." – Sapa