The source, who asked not to be identified, said Tsotne Gamsakhurdia was arrested at the Tbilisi airport.
"We detained him [Wednesday] when he flew into the airport," the source said.
Tsotne Gamsakhurdia was charged in late 2007 with an attempted coup and links with Russian security services after opposition protests against Saakashvili.
Saakashvili came to power in the 2003 Rose Revolution and shocked Western allies when he used riot police to crush the protests in November 2007. Georgian authorities said they had foiled a coup and accused Russia of stirring up disorder.
Tsotne's father was president of Georgia from 1990 to 1991.
A Message from The Moscow Times:
Dear readers,
We are facing unprecedented challenges. Russia's Prosecutor General's Office has designated The Moscow Times as an "undesirable" organization, criminalizing our work and putting our staff at risk of prosecution. This follows our earlier unjust labeling as a "foreign agent."
These actions are direct attempts to silence independent journalism in Russia. The authorities claim our work "discredits the decisions of the Russian leadership." We see things differently: we strive to provide accurate, unbiased reporting on Russia.
We, the journalists of The Moscow Times, refuse to be silenced. But to continue our work, we need your help.
Your support, no matter how small, makes a world of difference. If you can, please support us monthly starting from just $2. It's quick to set up, and every contribution makes a significant impact.
By supporting The Moscow Times, you're defending open, independent journalism in the face of repression. Thank you for standing with us.
Remind me later.