Rohit Shekhar Tiwari was ND Tiwari's son, the court had ruled in 2014. (File)

Rohit Shekhar Tiwari, who fought a six-year-long battle in court to prove that he was former Uttar Pradesh chief minister and Congress stalwart ND Tiwari's son, has died at 40 of a cardiac arrest.

"Rohit Shekhar Tiwari, a resident of Defence Colony, was taken to Max Hospital by his mother. He was declared brought dead," senior police officer Vijay Kumar said, adding no external injuries were observed on his body.

Rohit's mother Ujjwala Tiwari was in Max Hospital for her treatment when she received a call from home that he was unwell and bleeding from his nose. She then took an ambulance that brought Rohit to the hospital, the police officer was quoted as telling news agency IANS.

Rohit fought a long battle to get his father ND Tiwari to acknowledge him.

ND Tiwari had refused to give his blood sample for a DNA test in 2012. He, however, relented later.

In 2014, the Delhi High Court declared ND Tiwari as the biological father of Rohit Shekhar, after the senior leader accepted that he was indeed his son.

The court also restrained Mr Tiwari from denying in public that Mr Shekhar was not his son.

After hearing the verdict, Mr Shekhar's mother broke into tears while he appeared calm and composed.

The same year, ND Tiwari, aged 88, married Rohit Shekhar Tiwari's mother.

In 2017, ND Tiwari had met BJP chief Amit Shah but decided to stay in Congress, his lifelong party.

After ND Tiwari's death on his 93rd birthday last year, Rohit Shekhar Tiwari had demanded that the government at the centre, in Uttar Pradesh and in Uttarakhand build memorials and name schemes in the memory of his father.