Karnataka Chief Minister Siddaramaiah's son, Rakesh Siddaramaiah, died of multi-organ failure at a hospital in Belgium on Saturday, official sources said.
Rakesh, 39, had been suffering from a pancreatic ailment and was undergoing treatment at Antwerp University Hospital in the Belgian city, where he was admitted on Tuesday after developing sudden health complications.
Official sources in chief minister's office in Bengaluru said that he died of "multiple organ failure".
Siddaramaiah, his wife Parvathi, younger son Yathindra Siddaramaiah, who is a doctor, and the family doctor, who are already in Brussels, are likely to bring Rakesh's body back to India on Sunday evening.
Prime Minister Narendra Modi expressed his condolences and has requested the Indian Ambassador to Belgium to assist Siddaramaiah's family in carrying out the legal formalities in bringing the body back to India.
"My thoughts are with Siddaramaiah ji and his family on the demise of his son. May God give the family strength to bear the irreparable loss," he said in a tweet.
Congress President Sonia Gandhi expressed her shock and deep anguish over Rakesh's death.
"The entire Congress party stands with him (Siddaramaiah) and his family in this moment of loss. I pray for the peace of the departed soul and hope that the almighty gives strength to the bereaved family," she said.
Congress Vice President Rahul Gandhi also expressed his condolences. "My heartfelt condolences to Siddaramaiahji on the passing away of his son. My thoughts and prayers are with his family in this time of grief," he tweeted.
BJP's Karnataka unit president and former Chief Minister B.S. Yeddyurappa tweeted. "Heard the shocking news of demise of Rakesh Siddaramaiah. Deepest condolences to Sri Siddaramaiah and other family members.@CMofKarnataka."
Indian cricket team coach Anil Kumble, who hails from Karnataka, tweeted: "My heartfelt condolences to CM of Karnataka Siddaramaiah on the loss of his son! My prayers for him and his family."
Former MP Naveen Jindal, Rajasthan's former Chief Minister Ashok Gehlot, and leaders cutting party lines also expressed condolences.
Rakesh, who is survived by his wife, a son and daughter, was on a tour of France and Belgium with his friends when he developed the medical complications stemming from a previous illness caused by an accident he had been in 15 years ago.
After his birthday in July 2015, Rakesh had said that Siddaramaiah had clearly told him that he could not contest elections while his father was active in politics.
In an interview to a local Kannada news channel on his birthday occasion, Rakesh said he would enter politics and contest elections after his father retired, as he did not want people accuse the ruling Congress of becoming a 'father-son party' like the Janata Dal-Secular, a regional party run by former Prime Minister H.D. Deva Gowda and his son and former state Chief Minister H.D. Kumaraswamy.