Hi Mary Ann!
On the Felix at Oxford U thread, Nikolai wrote:
"Someone asked of Felix's London address and I don't see the answer. It was 15 Parkside, Knightsbridge. He returned to it after his escape with his Rembrandts and jewels after his rescue from The Crimea. but he soon had to let it go as he could not pay the rent and he wanted to live in Paris anyway."