A secret alliance is much easier to hide than a ten-year-old boy.

We must stand together, without appearing to do so, in secret alliance.

Their real purpose was dictatorship over the world, and so they soon formed a secret alliance with the Prussian government.

Unless he made some secret cautionary alliance of his own.

An example would be a secret alliance between two nations to support each other in the event of war.

"Or maybe a secret alliance with the Klingons, stretching back who knows how many years?"

Maybe he's setting up secret military alliances for an assault on Kaitain.

However, four individuals form a secret alliance to challenge the government's power.

He chose Arthur as they have a secret alliance.

Therefore Chile interprets this pact as a secret alliance against them.