Knox and Sollecito were found guilty Thursday of the 2007 murder of Kercher, Knox's roommate while they lived in Italy as exchange students.
Sollecito, who was in neighboring Austria with his girlfriend at the time of the conviction, was sentenced to 25 years in prison Thursday, CNN reported.
Sollecito said he returned to Italy "as soon as I understood the verdict."
"I'm trying to be as positive as possible in a situation like this," he said. "It's very traumatic, the situation here now. But on the other side, I still have to fight. I have chosen to be here and to fight against this ordeal."
After Thursday's conviction, Knox, who now lives in the United States, said she "will never go willingly" back to Italy.
Another man, Rudy Guede, was convicted in a separate trial and sentenced to 16 years in prison.
Guede, who fled Italy after the murder and was later extradited from Germany, has admitted he was in Kercher's room that night but denies he killed her.