The fiancee of lottery winner and transgender LGBT rights campaigner Melissa Ede says she has been “completely devastated” by her death.
The 58-year-old, who won £4m on a lottery scratch card in 2017, died on Saturday night, police said.
Her partner, Rachel Nason, said she found her slumped in a car at their home, near Hull, after a heart attack.
Ms Nason described her fiancee as “clever”, “funny” and an inspiration to others.
Posting on Facebook, Ms Nason said a post-mortem examination showed her partner had ischemic heart disease, which led to “a sudden heart attack”.
The former taxi driver went out to get cigarettes but shortly afterwards Ms Nason noticed her car engine revving.
Describing her rescue attempt, Ms Nason said: “I ran to it and started shouting ‘Mel, wake up’ but she didn’t even flinch.
“I put my hand on her chest and ear near her mouth but could feel no heartbeat or hear no breath.”
She said she dialled 999 and started performing CPR, before paramedics arrived.
Ms Nason said the lottery winner suffered from minor symptoms all week “like arm ache, fatigue and lots of burping”, since going into hospital on 5 May when she received “the all clear” from medics.
But she “didn’t feel ill enough to visit a GP”, she said.
“Mel obviously didn’t know she had this otherwise she would of sought medical advice.
“It’s completely devastated so many of us and to be taken so suddenly and unexpectedly is heartbreaking.”
Ms Ede’s funeral is due to take place on 30 May in Hull.
Before scooping the jackpot, she was known for her TV appearances and posting videos of herself online, attracting thousands of social media followers.