Euronews correspondent Galina Polonskaya was on the plane with Russian opposition leader Alexei Navalny before he was detained on arrival at a Moscow airport.
She described the journey from Berlin, where the leading Kremlin critic had been treated for a nerve agent poisoning, back to Moscow where authorities had warned that a defiant Navalny would face immediate arrest.
Polonskaya said the press who were waiting for Navalny and his wife, Yulia Navalnaya, to arrive at the airport in Germany for their flight were not briefed on how events were going to unfold and it was the politician's security detail who checked the couple in at the airport.
They made their way up to the plane flanked by security guards where the rest of the passengers had already borded.
On the plane, she said Navalny seemed relaxed and was joking with reporters during the flight.
When a fellow passenger gave him a small bear made of chocolate, he humorously suggested it might be poisoned.
Someone shouted to him asking if he was afraid of being arrested he laughed and replied: "Me, arrested? Why should I be arrested?"
The activist has said Russian authorities were behind the attempt on his life and investigative media have backed this claim, but Moscow has repeatedly denied the allegation.
He refused to give any interviews on the plane, instead watching cartoons with his wife.
But when there was an announcement that the plane was being diverted from its planned destination to another airport in Moscow, the atmosphere changed, according to Polonskaya.
The pilot first announced a delay of 30 minutes before indicating that the plane was heading for Sheremetyevo and would not land at Vnukovo airport as scheduled due to a "technical problem".
Navalny told his team that he had not expected this to happen, adding: "This shows to what extent they are afraid of me".
Crowds of his supporters, journalists and riot police units had gathered waiting for him at Moscow's Vnukovo airport.
When the plane arrived at Sheremetyevo, Polonskaya noticed for the first time that Navalny was holding his wife's hand. Navalnaya had been with the politician throughout his recovery in Germany.
"I felt like he knew what was going to happen," the correspondent said, referring to his impending arrest.
Then, with journalists swarming around him, Putin’s most prominent and determined critic gave a statement brushing off concerns about being arrested: "I know that I'm right. I fear nothing," he said.
When Navalny entered the airport building he was stopped at passport control and detained, with border police declining to respond when he asked what the reason was for his arrest, simply telling him it was a "border control issue".
His lawyer and his wife were not allowed to go with him, so after kissing Navalnaya goodbye, he was escorted away.
The activist asked for his lawyer to go with him, but the officers rejected his request.
The Russian prisons service said Navalny would be held in custody until a court rules on his case.
No date for a court appearance was immediately announced.
The service earlier said that it would seek to have Navalny serve his 3.5-year sentence behind bars.