The Welsh student, 22, gave his first interview during Love Island spin-off Aftersun on Sunday.
Speaking to show host Laura Whitmore, he said he knew Gemma Owen had not been feeling it after the public vote matched them together.
Also, the rising star expressed his surprise after finally finding out her dad is former England footballer Michael Owen.
Speaking via video link from Newport, he said: "I was buzzing when I coupled up with Gemma. I got the feeling her head was elsewhere. I can’t believe who her dad was. I can’t believe I didn’t work it out.
"It’s crazy. I didn’t expect the support. It’s a big eye-opener for me how many people were on my side and had my back. I was looking at Gemma when I walked in and hoping it was her I would couple up with."
Scenes shown on Friday saw Llewellyn gather the islanders around the fire pit to tell them of his decision to leave.
He emphasised his decision to leave the ITV2 dating show not been taken lightly.
He said: "Trying to find someone to leave the villa with, that you care about, obviously that’s the goal. But when you’re not feeling that, it sort of makes it very hard.
"I’ve been thinking long and hard about this. It’s not a spur-of-the-moment type thing. So I’ve made a decision that I am going to leave the villa. It’s been a breeze, it’s been an absolute ball, you are all unreal."