Tarek Khalaf Abdullah, the right-hand man of ISIS "caliph" Abu Bakr al-Baghdadi, was reportedly killed by the Syrian Army on May 16.
Abdullah was one of ISIS most prominent field commanders inside Syria, according to AhlulBayt News Agency. Abdullah was also known by his nom de guerre, Abu Hatem Albu Umar.
He was known as one of Baghdadi's most loyal subordinates, and led several operations against the Syrian Army and the People's Protection Units in Kurdistan.
Abdullah's death is ill-timed for the terrorist group, as ISIS forces face a serious threat from the Iraqi Army on multiple fronts, including at the Al-Qa'im border crossing and in the city of Mosul.
Local sources from Iraq have indicated Baghdadi has returned to Iraq from Syria and is hiding in the country's Nineveh province. The move apparently comes as ISIS is under continuous attack from Syrian, Russian and Iraqi air forces in western Iraq and eastern Syria.
AhlulBayt News Agency reports that Baghdadi had been moved from Turkey to Libya in early March 2016 after he was tracked down and allegedly targeted in Iraq and Syria on numerous occasions.
Sources in Libya say Baghdadi was there in December when he arrived in Sirte, the hometown of the former Libyan dictator Moammar Gadhafi.
"While everyone is looking for him in Iraq and Syria, no one expects him to be in Sirte," according to the Libyan source.
"If he is to be exposed to danger, Sirte would be the last place on Earth for his life to be endangered as it is the safest Takfiri stronghold in the world."
The Syrian Army, the National Defense Forces, Hezbollah, the Syrian and Russian air forces, and the Iraqi armed forces have recently been conducting large scale operations in Iraq and Syria to end ISIS' grip on territory in both countries.