The proboscis monkey, better known as the long-nosed monkey is endemic to the island of Borneo. I'm not the greatest at identifying animals, but I believe this is one of the long-nosed monkeys based on my tour itinerary and location, although admittedly this monkey's nose doesn't look that big. Perhaps someone better suited to identifying monkeys will be able to correct me here.
There's only so many different types of monkeys in Brunei, but you can easily see them from a distance when taking a water taxi around Bandar Seri Begawan. In my case, I was transiting to the so called 'Venice of the East', Kampong Ayer which is a short ride away.
Just a monkey sitting in a tree.