In his Chess Note no.4360, Both stood up, Edward Winter gave several versions of an apocryphal anecdote concerning the first two candidates for the title of World Champion. Here's the Irving Chernev version:-
Steinitz and Zukertort were once present at a dinner where a toast was given to the "Chess Champion of the world". Both players stood up.
After the great 1883 London Tournament, both players had a legitimate claim to the title. The incipient challenge over the next few months was recorded by the British Chess Magazine (BCM), starting with an article 'Some Aspects of the Two Tournaments' (i.e. the 'major' and 'minor' tournaments).
Counting from the end of the 1883 London event, where Zukertort won the 'major' tournament in June, more than two and a half years would pass before the start of the first recognized World Championship event, the 1886 Steinitz - Zukertort Title Match.