The US president made the joke to photographers and cameramen from the Singapore government’s television channel Host TV at the historic Singapore summit on Tuesday.
Mr Trump said: “Getting a good picture everybody? So we look nice and handsome and thin, and perfect”.
Mr Kim looked visibly ruffled by the remarks and could be seen frowning as cameras zoomed in on his face.
The pair met one-on-one for just under 40 minutes before going on to an expanded meeting with other officials and a three-course working lunch.
Mr Trump and Mr Kim concluded an extraordinary nuclear summit with the US president pledging unspecified “security guarantees” to the North and Mr Kim recommitting to the “complete denuclearisation of the Korean Peninsula.”
When they first arrived for the landmark summit at the Capella hotel on Sentosa – a resort with luxury hotels, a casino, manmade beaches and a Universal Studios theme park – the leaders appeared initially cautious.
But Mr Trump, who described Mr Kim as “very smart” and a “very worthy, very hard negotiator”, said he had formed a “very special bond” with Mr Kim and that the US relationship with North Korea would be very different.
Mr Kim’s grimace over Mr Trump’s gag about weight comes after the White House gained headlines last month after releasing a commemorative coin which featured a slimmer-looking Mr Trump head to head with a rather larger Mr Kim.
The item was minted by the White House Military Office which designs coins for Mr Trump’s trips abroad. It displays profiles of Mr Trump and Mr Kim in front of US and North Korean flags beneath the heading “peace talks” written in English and Korean.
It describes the latter as “supreme leader”, which is a term commonly used to refer to Mr Kim albeit it not being his official title.
The coin, which was widely mocked on social media, accentuated the rolls of spare flesh around Mr Kim’s neck, which the casting has carefully picked out with little creases.
The US President taunted Mr Kim last November by saying he would never call him “short and fat”.
“Why would Kim Jong-un insult me by calling me ‘old’ when I would NEVER call him ‘short and fat’?” Mr Trump tweeted. “Oh well, I try so hard to be his friend – and maybe someday that will happen!”