LONDON -- Ukrainian President Volodymyr Zelenskyy said he'd arrive in London on Monday for "substantive" talks with Prime Minister Rishi Sunak.

"I will meet my friend Rishi. We will conduct substantive negotiations face-to-face and in delegations," Zelenskyy said on Twitter.

The surprise visit comes a day after Zelenskyy made a surprise visit to Paris for talks Sunday night with French President Emmanuel Macron.

This is a developing story. Please check back for updates.

ABC News' Angus Hines contributed to this story.