Does Darius Trifarian ready himself when he's the second card played in a turn?

Ruling: Yes, Darius Trifarian readies himself when played as the second card in a turn.

Sequence:

• A card is considered "played" when it fully resolves
• Darius enters the board as part of his resolution
• Darius is already on the board when his "after you play a second card" ability checks
• His ability triggers and readies himself