I think these have been the most difficult four months in my life, but after today I feel much, much better," said De Palo.
The victory capped off a highly competitive weekend for the rookie.
He also finished fourth in Saturday's sprint race after being overtaken for a podium position on the final corner.
"A very good weekend here at Silverstone.
We knew we had the pace since Free Practice because we have always been at the top, so we are pretty happy for our work done at home to prepare for this race.
It's the result of the work done with my engineer, with my coach, and all the McLaren staff, so we are pretty happy about what we are achieving together," said De Palo.
"It has not been an easy start to the season, we had a lot of issues, but we were keeping our faith that we were going to do a strong year together and this is the result this weekend, so really happy.
Starting from P5 is not a guarantee that you can get this win, so doing it like this is even better," he added.
De Palo had already noted his team's underlying capabilities following his strong performance during the shorter sprint event the previous afternoon.
"We knew that this was our potential," said De Palo.
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"We've been really lacking in the previous races, but we managed to put it all together this week."
