A keen footballer and good student, Letts admitted to his parents that he was with ISIS in Syria in September 2014.
The parents of a white British Muslim convert dubbed "Jihadi Jack" were on Wednesday charged with terrorism offences for making money available for their son who left the UK to join the ISIS in Syria.
Jack Letts' father John, 55, and mother Sally, 53, have been charged with three counts of entering or becoming concerned in an arrangement to make money available, knowing or having reasonable cause to suspect that it may be used for terrorism.
They will appear at Westminster Magistrate's Court in London on June 9.
The couple had said the money was for their 20-year-old son to buy a new pair of glasses when they were arrested earlier this year.
"Even if you know he's in danger or can't see straight, what parent isn't going to try get their child a pair of glasses if he can't see straight," John Letts had told 'Channel 4 News' in an interview in February.
The couple have said there was no evidence their son had become an ISIS fighter and claimed the police have "put two and two together and made 10".
"He has the freedom to practice whatever he wants, that's British values. It's so unfair, but if there is any evidence that he's done anything violent, if anyone can prove any of these allegations... if you can show me any of that I'll be the first to believe it and I'll be the first to report it," Jack's mother Sally said.
Jack, who attended Cherwell School in Oxford, converted to Islam as a teenager and left his home to travel to the war-torn country of Syria over a year ago.