Lee Kun-hee, the de facto head of South Korea's top conglomerate Samsung Group, is set to celebrate his 75th birthday at a local hospital with his family later this week, sources said Thursday.

Lee, the wealthiest man in South Korea, turns 75 on Saturday.

After suffering a heart attack on May 10, 2014, he was rushed to Samsung Medical Center, a group hospital, where he underwent stent placement and has remained since.

While various rumors surrounding his health continuously caused the local financial market to fluctuate, Lee is now presumed to be in stable condition, especially after a photo of him lying on a bed at the hospital's VIP room was revealed in June.

Samsung currently declines to comment on the details of Lee's condition, only to repeat that he is "slowly and gradually recovering."

Lee had delivered speeches on yearly business guidelines for the group and held ceremonies with CEOs around his birthday annually before falling ill.

His only son, Jae-yong, currently takes the role as the de facto heir but has yet to take over fully.

Samsung Group has Samsung Electronics Co., the world's leading maker of smartphones, memory chips and TVs, under its wing. (Yonhap)