The 25-year-old singer was introduced to the prince at the premiere of James Bond movie 'Spectre', for which he sang the theme song 'Writings On The Wall', and he went a little too far when he bowed to the 33-year-old royal.
Speaking on 'Watch What Happens Live With Andy Cohen', he said: ''I've met him a few times... They told me to bow. And I thought when you bow -- I really bowed. I was at a right angle. It was like I was going to suck his d**k.''
The 'Too Good at Goodbyes' singer thinks it is ''great'' that Harry recently got engaged to former 'Suits' actress Meghan Markle.
He was asked by presenter Andy: ''Initial reaction to Prince Harry and Meghan Markle's engagement given your love for that gingy?''
He laughed and replied: ''For that gingy!? Yes. I think it's great.''
The 'Stay with Me' singer recently admitted it would be a ''dream'' to perform at Harry and Meghan's wedding next year.
He gushed: ''I'm obsessed. I want to sing at the wedding. Oh my God I'd love to, it would be a dream.''
Sam - who is in a relationship with '13 Reasons Why' star Brandon Flynn - also recalled how he was ''running around London with a flag'' in 2011 when Harry's brother Prince William married Catherine, Duchess of Cambridge.
He revealed: ''I woke up at 6am, downed a bottle of wine and went and sat in Hyde Park. I was wasted the whole day, running around London with a flag. I was just screaming when she walked out in that dress.''
From 'Happy' to 'Banana Pancakes', these are soaked in positivity.