A marquee free agency signing in the 2025 off-season, De Koning joined the club he supported as a boy after eight seasons at Carlton. The 201cm ruckman's athleticism gives St Kilda a genuine two-pronged ruck division alongside Rowan Marshall, and he kicked his first Saints goal on the three-quarter-time siren in Round 6, 2026. He has played 120 AFL games and kicked 47 goals.