1. Readying up for a short stroll with my dad, we were in the front yard when we saw it. Cloudless day in April. 2. We regularly watch airplanes, and this time we noticed something strange3. An F16 of the Dutch airforce. Highly irregular event next to a passenger airplane, but possible. Next moment it dawned on us that it couldnt be a F16 because lack of contrail and wings. The size was roughly one-third of the airliner. Color was same tint as the airplane. As all airplanes on that altitude seem to have to the naked eye.4. It had the same speed of the airliner when it 'hovered' next to it, seemed to be at the same altitude as the airliner, about five seconds like that and then it suddenly slided forward in a fraction of a second, to abruptly adopt the same speed as the airplane again. Roughly ~800m in front of the airplane, rightside. It stayed like that for a few seconds then it took off again in Western direction at great speed and apparently instant acceleration. Within 9 seconds it was gone in the horizon. It was a sunny day, it shimmered very brightly for about two seconds while it was on high speed darting off to the West. 5. My mom and dad were the other witnesses. They were as confused as I. In the months after, I started having to have very vivid dreams about UFO's in the nightly sky while looking through my window. Also observing triangle UFO's. All in my dreams. Never been as vivid as before. It's like my subconscious trying to place this event.6. Horizon, it darted off until it was a black dot and then nothing. It disappeared by sheer distance.