The answer is the strong nuclear force.
After having looked at Feynman diagrams online for similar interactions I figured out an interaction for this one that I have drawn above. Is that correct? I believe I understand the interaction that I have drawn but I don't understand why it's impossible to be any other type of interaction.
As K+ has a strangeness of +1, X must have a strangeness of -1 to conserve strangeness. I know strangeness can change by +/-1 in weak interactions, but as we know X has strangeness, it must have a strangeness of -1 to satisfy strangeness not changing, or changing by +/-1.
X must be a baryon to conserve baryon number and it must have a charge of +1e to conserve charge.
So, it therefore has three quarks, one being a strange quark, and the other two must be either up, charm or top quarks to conserve charge.
Why must it be two ups (if it even must be that)? If a quark changed flavour from an up to something else the weak force would be in play. Is that a possibility?