Millionaire Haakon Overli, 52, began an affair with the woman after she arrived at the family home in Surrey following the Russian invasion.
Now, the entrepreneur has left his wife and moved in with his mistress, the paper reported.
He had repeatedly tweeted his support for bringing Ukrainian refugees to the UK at the beginning of the conflict in March.
Norwegian-born Mr. Overli, who has an economics degree from Durham University, made his money in the dot-com boom after founding online stockbroker Self Trade in 1997, selling it for more than £900 million in 2000.
He also worked for JP Morgan and ING Barings and served as a director at Wonga for a year in 2008.
It fell into administration in 2018 after being heavily criticized for ‘predatory lending’ to people who would never have been able to repay the loans.
Around 200,000 customers owed £400 million when Wonga went bust in a flood of compensation claims.
After his time at Wonga, Mr Overli co-founded software investor Dawn Capital, now worth more than £2 million.