Sophie was in full make-out mode in London Friday with her new boyfriend, British aristocrat Peregrine Pearson -- no worries on pronunciation ... he goes by Perry.

S&P strolled down the streets of London, hand in hand, as they made it clear to one and all -- they're a couple.

We actually saw the 2 back in October kissing each other in Paris ... but it was unclear if they were in a relationship. Now it's crystal clear.

As for his lineage ... Perry is the eldest son of Michael Pearson, the 4th Viscount Cowdray -- also a major stakeholder in the Pearson family media empire.

Sophie's loaded -- $10 mil -- but it pales in comparison to Perry, whose bank is north of $270 mil.

As TMZ reported, Joe Jonas filed for divorce back in early September, and it was acrimonious from the jump, although things seemed to have calmed down.

As for Perry, he's coming off a relationship with King Charles' goddaughter, Princess Maria-Olympia of Greece and Denmark.

Joe and Sophie have reached a temporary child custody agreement, where their 2 kids will travel back and forth from the U.S. to the U.K., although no permanent arrangement has been struck.