Slipstream vs Countercharge timing

[Aerospider]

Suppose a Seraph puts up its Slipstream animus and advances to within six inches of something with Countercharge. He wants to use Slipstream to place a model in melee with the Countercharger before the Countercharge takes place (and thus prevent it altogether).

What's the timing of events in this situation?
Does the Slipstream go first because it belongs to the active player?

[DarkLegacy]

https://privateerpressforums.com/showthread.php?62691-Countercharge-vs-Slipstream

[Aerospider]

Thanks. Ten.