Tristan blacked out while hugging Zhen-Zhen from behind. But it was just temporary as he regained his consciousness right after.
However, Tristan was no longer the one in control of his body. He was possessed by Mheera's soul. Through the forbidden spell, she merged her soul into Tristan's body using the mark she left in his system.
Upon leaving her own body, Mheera's soul was sent to Tristan's location thus merging into his body without his knowledge.
The proposal and his surprise for Zhen-Zhen was going smoothly but it was interrupted by Mheera. She was now the one taking over Tristan's body.
A cold glint flashed in Tristan's eyes as he gazed down at Zhen-Zhen who was leaning on him.
Zhen-Zhen noticed that something strange happened to Tristan as he just suddenly became quiet.
She was about to ask him when in one swift move, Tristan locked her head using his arm. He was strangling Zhen-Zhen from behind.