Cabal/Farah won 3 titles earlier this year partnering in doubles.
They already won 6 doubles titles this year! They are leading that category together with Treat Conrad Huey, who also won 6 doubles titles (with 6 different partners!)
Another interesting fact about Denis Istomin: Not only did he win 4 titles in 4 finals, those were also the only 4 challenger tournaments that he played this year! So that means he's currently on a 20 match winning streak on challenger level.