This is excellent and puts you in a relatively strong position. Your boss is new in his role, and wants to deliver, and knows he can rely on you.
I would start by understanding exactly what your current package is. Holiday allowance, medical insurance, bonus, share options, travel time, travel expense, are you heading towards a parish, or bonus currently that you'd lose if you left? Every little detail. Have a think about the things you might be negotiable on. For example, you may travel more for an extra 10k, or maybe not?
When speaking to your boss, say something like "I'd love to work with you again, let's talk terms".
If there are stock options in the new place, think about whether that would be of interest. Have your bottom line in mind too. There is a rude reality of paying bills, so you need a minimum position.
What is the industry average for your role? Is the new company a high payer or not? What have your successes been? What have you delivered?
I'll probably think of more, but the more armed you are about your own worth, the more confident you will be. The first point is the main one though. He wants you as he knows he can rely on you. That is worth money. His budget won't be unlimited, so leave yourself room for negotiation. I usually go along the lines of "I was thinking of a headline number of £xx but it depends on the whole package". That gives you wiggle room.