Filhol, a 53-year-old Frenchman, has been on the road for 20 years and often works with players for free.
World number two Roger Federer eased past unseeded Italian Andreas Seppi 7-6, 6-4 to claim a record-extending eighth Halle Open title.
The Swiss top-seed was unable to break the Italian’s serve in the opening set, winning it in a tie-breaker.
The year 2013 was difficult, 2014 was better and now 2015 after this week is even better
Seppi, who reached his second final of the year after Gael Monfils and second-seed Kei Nishikori retired in his two previous matches, earned another break opportunity at 2-2 but he sent a backhand into the net.
World number two Federer then squandered three breakpoints at 4-3, allowing Seppi to hold on and win the 10-minute game.
He did everything right, however, two games later to earn two match points and finished off the contest with a spectacular overhead smash.
“It is a special moment for me, to win this tournament an eighth time,” the 17-time grand slam winner said courtside.
“I have always enjoyed amazing support here all these year. I always enjoy it here and it is one of my favourite events.
“The year 2013 was difficult, 2014 was better and now 2015 after this week is even better and I hope I can keep it up.”
Federer, the defending champion here, has now won Halle more times than any other tournament.
The win also gave him a fourth title this year after victories at Istanbul, Dubai and Brisbane to take his career haul to 86.