Sulaiman al-Subaie, 25, who grew popular in his homeland for his posts on video-sharing app Keek, reportedly joined ISIL, the most radical group fighting in Syria, last August.
"The situation in Syria is not as portrayed in the media," Subaie said in a rare interview aired on Saudi television late Wednesday.
"What is amazing is that Saudis are killing fellow Saudis in the fighting between ISIL and al-Nusra Front," the al-Qaeda franchise in Syria.
ISIL, disavowed by al-Qaeda chief Ayman al-Zawahiri, has been accused by militants battling Syrian government forces of seeking to consolidate power rather than other things.
Fierce clashes between ISIL and rival militants broke out in early January, after accusations that the terrorist group was abusing both civilians and rival insurgents.
The fighting has left hundreds dead and created openings for government advances in some areas.
Subaie said in his "confessions" that the death of his brother, a militant, had prompted him to join the war.
"I went to Qatar, from where I traveled to Turkey" before being led into Syria with the help of a smuggler.
He wanted to join al-Nusra Front but "upon my arrival, I was told that I have now become a member of ISIL," he said.
Subaie claimed that he decided to quit the group after realizing that his Twitter account, followed by thousands in Saudi Arabia, was being used to broadcast "messages inciting" violence against rulers and clerics in Saudi Arabia.
He fled back to Turkey and returned to the kingdom, where he is being held.
There are no official figures on the numbers of Saudis who have joined terrorist ranks in Syria, but they are estimated at several hundred.
The Wahhabi kingdom has been a key backer of the three-year battle against the Syrian government.
But King Abdullah last month decreed jail terms of up to 20 years for citizens who travel to fight abroad, as the country struggles to deter young Saudis from becoming terrorists.
In 2011, Riyadh set up specialized terrorism courts to try dozens of Saudis and foreigners accused of belonging to al-Qaeda or of being involved in a wave of bloody attacks that swept the country from 2003.
The interior ministry urged those wanting to "repent" to turn themselves in at Saudi embassies, saying they would be repatriated and reunited with their families. But Subaie's fate was not announced.
BA/BA