Sir Mark Thatcher has left South Africa after pleading guilty over his involvement in an alleged coup plot in Equatorial Guinea.
Sir Mark can now leave South Africa
The son of former UK Prime Minister Margaret Thatcher was fined the equivalent of US$500,000 (£265,000) and given a four-year suspended jail term.
Sir Mark, who denies any knowledge of the plot, agreed a plea bargain and will now co-operate with investigators.
He left Cape Town on a flight to London's Heathrow on Thursday evening.
Sir Mark admitted breaking anti-mercenary legislation in South Africa by agreeing to finance a helicopter.
The businessman said he did not initially know the helicopter's alleged purpose - that it was to be used in the alleged coup attempt, instead believing it was to be used as an air ambulance.
But in his plea bargain statement, Sir Mark says he came to realise the helicopter was to be used for mercenary activities before the deal was finalised.
Speaking outside court, an emotional Sir Mark said: "There is no price too high for me to pay to be reunited with my family and I am sure all of you who are husbands and fathers would agree with that."
Baroness Thatcher also expressed her relief at the outcome, saying: "This has been a difficult time for all of the family - obviously I am delighted that it has been brought to an end.
"I know that what matters to Mark now is to be reunited with Diane and the children as soon as possible."
Her son is now leaving South Africa for the first time in five months.
An advisor to Equatorial Guinea's President Teodoro Obiang Nguema Mbasogo told the BBC's Focus on Africa programme that: "We are confident that justice has been done," implying that they would no longer seek Sir Mark's extradition.
The BBC's Alastair Leithead said it seemed Sir Mark could now turn "state witness" as part of his co-operation with the South African authorities.
If Sir Mark had been unable to pay the three million rand fine, he would have incurred a five-year prison sentence, with his four-year suspended sentence on top of that.
Meanwhile, the Zimbabwean lawyer for a close friend of Sir Mark accused of leading the alleged coup plot, former SAS officer Simon Mann, says that his jail term has been reduced from seven years to four by a court in Harare.
Mann was last year found guilty of illegally buying weapons in Zimbabwe, which were allegedly intended to be used in the Equatorial Guinea coup plot.
A further 14 men were found guilty in Equatorial Guinea of being involved in the alleged plot to overthrow President Nguema, who has ruled Africa's third-largest oil producer for the past 25 years.
Nick du Toit was jailed for 34 years, while opposition leader Severo Moto, who is in exile in Spain, was given 63 years in absentia.
Both men escaped the death penalty demanded by the prosecution.
Sir Mark, 51, was arrested in August at his home in South Africa and released on bail.
News of Thursday's hearing in Cape Town came as a surprise. The defendant was not expected back in court until 18 February.
After his plea, his lawyers released a statement saying: "It should be noted that Sir Mark was not charged with any involvement in the attempted coup d'etat in Equatorial Guinea.
"The plea bargain was entered into solely as a result of his financing of the charter of a helicopter in circumstances where he should have exercised more caution."
Sipho Ngwema, a spokesman for South Africa's Directorate of Special Investigations, also known as the Scorpions, said Sir Mark had promised to co-operate with South African investigators.