"You said you would buy a house when you had the money. Well now you have the funds, we both know that, but you don't want to do it."
The prince replied: "I'll do it, you'll have half of all my things, like I promised."
He lavished gifts on her, including a Mercedes worth €83,000 ($139,000), a ring worth €100,000 ($167,000), luxury holidays around the world, a share in a boutique hotel worth €58,000 ($97,000) and cash payments of around €500,000 ($837,000).
The battle between the two emerged last week when it was revealed that the prince had launched legal action against Yashenko, accusing her of taking advantage of him while he was in a fragile mental state as a result of divorcing his wife.
He has accused her of "circonvenzione d'incapace", an Italian legal term which means "exerting undue influence over persons who are non compos mentis."
Yashenko has denied any wrongdoing and has insisted that the prince withdraw his accusations.
Further complicating the feud, Yashenko accused the prince of stalking her last year.
At one point she wrote to him: "I asked you not to bombard me and yet you send me thousands of emails."
In a further twist, the prince wrote a message on his Facebook account at the weekend, saying he wanted to "publicly apologise to my partner Tanya Yashenko for my false statements. I would like to explain that jealousy is a big reason for my actions. But the gifts I gave I don't want back."
The aristocrat, who was educated in the US, added: "My Italian isn't good considering I've lived abroad all my life. I apologise for my mistakes."
In a second message on Facebook, posted on Sunday, the prince wrote: "I love her. A flower that makes me feel calm. I'm a lucky man."
But his lawyer said those statements should not be taken at face value. The prince was under huge pressure from Yashenko, said Armando Fergola.
"She continues to try to manipulate him. He has certainly not withdrawn his accusations and will not do so," he told The Telegraph.
"He is still very fragile and the love affair has clouded his judgment. The primary aim of this case is to protect him from her, both psychologically and economically. Getting her to pay back the money is a secondary objective."