The Spanish king's brother-in-law began a six-year jail sentence on Monday, drawing a line under a long-running corruption scandal that enraged the public and brought shame on the royal family.
Inaki Urdangarin, the husband of King Felipe's sister Cristina, arrived at a prison north of Madrid early on Monday after losing an appeal at the Supreme Court last week.
The former Olympic handball player was sentenced to five years and 10 months of prison for embezzling millions of euros in a case which caused uproar and even contributed to the abdication of Felipe's father.
Urdangarin, 50, turned himself in at a facility near Brieva, about 100 kilometres (60 miles) north of Madrid, at 8:00 am (0600 GMT).
The move brings to a close a long-running scandal that has embarrassed the Spanish royal family.
Urdangarin went from being the golden boy who charmed the Spanish royals in the 1990s to the black sheep who tainted the royal family's reputation.
He was guilty last year of embezzling millions of euros between 2004 and 2006 from the non-profit Noos Institute sports foundation that he headed on the island of Majorca.
The probe first began in 2010 and the scandal really took off a year later when the royal family excluded him from its activities.
Urdangarin's jail term began as King Felipe VI was on an official visit to the United States where he will meet US President Donald Trump on Tuesday.
- A very public fall -
During an interview with public television TVE, Prime Minister Pedro Sanchez said Urdangarin's conviction and jailing showed that "no one is above the law and that the law is the same for all".
The case fuelled angry protests by Spaniards suffering hardship in an economic crisis.
Urdangarin was seen as a symbol of the elite's perceived corruption.
It also soured the end of Juan Carlos's reign.
He gave up the throne in June 2014, hoping his son Felipe VI could freshen up the image of the monarchy.
Urdangarin and Cristina eventually moved with their children to Switzerland.
In 2015, King Felipe VI stripped them of their titles of duke and duchess of Palma.
At the start of 2016, the pair went on trial in Majorca along with more than a dozen others. Urdangarin faced charges of embezzlement, influence peddling, forgery and money laundering.
In February 2017, he was found guilty of creaming off millions to fund a lavish lifestyle. The court handed him a sentence of six years and three months.
Cristina was tried on charges of helping her husband evade taxes while he headed of the Noos Institute. She was acquitted, but was fined 265,000 euros on separate charges on the grounds that she had benefited from her husband's wrongdoing.
- Lavish lifestyle -
Despite Urdangarin's sentence, he was allowed to remain free while pursuing an appeal to the Supreme Court. He lost that case last week, although the court reduced his sentence by five months.
The court also reduced Cristina's fine to 136,950 ($161,400) euros.
Cristina was the first member of Spain's royal family to face criminal charges since the restoration of the monarchy in 1975.
After marrying Urdangarin in 1997, she was constantly in the celebrity spotlight, winning praise for having a salaried job.
But eventually, eyebrows were raised at the couple's lavish lifestyle, including the purchase in 2004 of a six-million-euro home in Barcelona.
The royal family has made no comment on Urdangarin's conviction.
He will serve his term as an inmate of Brieva jail, which houses up to 162 prisoners and is mainly used for women.