Kanye West and Rihanna Tour (2015)
Though it was never officially announced, rumors flew throughout the winter of 2014–15 that West and Rihanna were gearing up to hit the road together. Between a tweet from RiRi about a "Kanye West Tour Experience" prize in her charity auction, a couple of premature postings by Live Nation and Ticketmaster that listed upcoming Kanye/Rihanna shows, and the fact that the two artists had recently collaborated on the song "FourFiveSeconds" with Paul McCartney, all signs seemed to point to a blockbuster tour.
And then ... nothing. Several gossip mags claimed that Rihanna (who had previously opened for West on 2008's Glow in the Dark tour) pulled out of tour talks because of her aversion to Kim Kardashian and worries that Kanye would "hijack" the whole thing, but we may never know for sure what really happened.