One year later he harbours the kind of ambition that could create a security nightmare for Egyptian authorities: to return home and hoist the Islamic State's black flag in Egypt as his comrades have over large swathes of Iraq and Syria.
Eventually, says Younes, he and other Egyptian fighters in Islamic State intend to topple Egypt's U.S.-backed government and extend their caliphate to the biggest Arab nation.
"We will not be able to change the situation in Egypt from inside, but Egypt is to be opened from abroad," Younes, who asked that his last name be withheld, told Reuters in an interview conducted by Facebook.
Reuters reached Younes by contacting supporters of Islamic State on social media networks. Another Islamic State fighter identified him as a militant in the group. Location tags on his Facebook messages placed him in Syria.
Egypt is well aware of the risks posed by its citizens going abroad for jihadist causes and then returning. Egyptians who fought Soviet occupation troops in Afghanistan in the 1980s eventually took up holy war at home, training their weapons on Egyptian security forces and carrying out bombings.
The chances of Islamic State militants establishing a caliphate in Egypt are slim: the Egyptian state has crushed one militant group after another.
But the return of fighters with experience in Iraq and Syria could certainly bring more violence and complicate efforts to stabilise a country that has suffered from political turmoil, with two presidents toppled since 2011.
Egyptian security sources say they are closely monitoring militants fighting abroad and have lists of their names at airports to arrest them on arrival.
Younes was a 22-year-old student at Cairo's thousand-year-old centre of Islamic learning, Al-Azhar University, when he decided to join the world's most dangerous militant group.
Like al-Qaeda leader Ayman al-Zawahri, a former physician, he came from a wealthy family living in Maadi, an upscale, leafy Cairo suburb. He learned about Islam at a young age from his mother but mostly shared the interests of any other Egyptian youth: a love for soccer and martial arts like Kung Fu.
Younes took part in the street protests which ended 30 years of iron-fisted rule under President Hosni Mubarak in 2011. But he also rejected the Muslim Brotherhood, the Islamist group that came to power after Mubarak. He calls Mohamed Mursi, the Muslim Brotherhood figure who became president until he was overthrown by the army last year, an apostate for opting for Western concepts like elections rather than radical Islamic rule.
The man who toppled Mursi, then army chief Abdel Fattah al-Sisi, now Egypt's president, was "even more blasphemous", Younes said. Sisi has promised to crush militants, including those inspired by Islamic State.
State security forces killed hundreds of Muslim Brotherhood supporters in the streets of Cairo after Mursi was toppled last year. But Younes said the bloodshed was not a factor in his decision to embrace Islamic State. His motivation was much deeper - a burning desire to topple Arab "tyrants" like Mubarak, Mursi and Sisi, and create a caliphate.
Younes was attracted to Syria because it had become a hub for militants from around the world with the ultimate goal of clearing their home countries "from the abomination of tyrants".
Joining Islamic State was not a straightforward matter. An Islamic State member had to nominate Younes after he proved himself in another militant group in Syria, where he arrived from Turkey.
"The Islamic State is not like the other factions. It does not accept anybody until he gets an endorsement from a member of the state," he said.
Eventually, he was trained by an Egyptian commander. Younes become a sniper, learned how to use heavy weapons at a camp in Syria and fought in major battles in neighbouring Iraq, he said.
Among the skills he was taught was the correct technique for beheadings. He said he had personally carried out such killings, but did not say who the victims were or how many he had killed. Those who were killed deserved their fate because they had participated in the killing of Muslims, he said.
Islamic State released a video on Tuesday purporting to show the beheading of American journalist Steven Sotloff. The purported executioner appeared to be the same British-accented man who appeared in an Aug. 19 video of the killing of another American journalist, James Foley.
Islamic State emerged from the Iraqi branch of al Qaeda. But unlike its parent organisation, which specialises in hit and run tactics and suicide bombings, it has evolved into a military organisation which seizes land and holds it its bid to expand the self-proclaimed caliphate.
"This is a state which has ministries and offices. The army is part of its pillars," said Younes. "There are brigades and battalions like any other army in the world."
Younes said there were about 1,000 Egyptians in Islamic State and he had met many of them. He identified one as Islam Yakan, a former rapper. "Thanks be to God for guiding him on the right path," said Younes, adding he was sitting beside him.
Asked if Islamic State is trying to recruit more Egyptians, he said: "Yes everybody tries to teach Muslims their religion and what God imposes."
Islamic State has attracted a following from Egyptian Islamists on social media sites. Egyptian security sources estimate there are up to 8,000 Egyptians fighting abroad with militant groups such as Islamic State and al Qaeda.
At home, Sinai-based Ansar Bayt al-Maqdis has become a major security problem, killing hundreds of police and soldiers and carrying out high-profile assassinations over the past year.
Egyptian militants based just over the border in Libya who are inspired by Islamic State have also established contacts with Ansar, security sources say.
"You should know that there are jihadi camps even in Egypt," said Younes. "Ansar Bayt al-Maqdis is a group of mujahideen seeking to apply Islamic Law on the land of God. We ask God to help them."
Younes said he had persuaded about 100 others to take up holy war before leaving on his own mission.
"Now, they are all Mujahedeen, thank God. Some of them became martyrs, some are still on the road. We ask Allah for steadiness and a good ending," said Younes. "Those in Egypt participate in attacks (against the army and police) and will continue until the arrival of the conquering state of Islam."
Younes said Islamic State members included thousands of foreign fighters. Like many others, he tore up his passport, an act of allegiance to Islamic State, which rejects borders.
"I will stay here in Syria until we conquer it and will come to Egypt to conquer it, God willing."