Hamilton brought the curtain down on his 14-year association with the team in Brazil on Sunday, sadly retiring on lap 55 after being hit by Force India's Nico Hulkenberg whilst leading.
It was an ignominious end to Hamilton's six years in Formula One with McLaren, which naturally left Whitmarsh gutted for the 27-year-old as he described his campaign as "full of ups and downs".
Aside from one final goodbye to the entire workforce at the McLaren Technology Centre in Woking this week, Hamilton's work is done with the team.
Asked as to how he felt about Hamilton's exit, Whitmarsh replied: "I'm very sad about it.
"I've known him personally for over 15 years, and seen him through some great, great moments.
"He's a great human being, a great asset for any team, so of course I'm disappointed he is going. It's emotional, but we're a tough team and we have to get on.
"We've the makings of a good car next year and we'll go out there and do our best.
"He's been a friend and a colleague for a long time. Next year he'll be a competitor and we'll try and beat him.
"I'm sure we'll continue to have a good relationship, we'll compete appropriately and we'll go out there and see how we get on."
Whitmarsh refused to look back with any regret on the negotiations with Hamilton and his management, XIX Entertainment, that led to him opting to snub a new McLaren deal and join Mercedes.
Mercedes sold Hamilton on a £15million-per-year contract, plus more freedom away from sponsorship commitments, an offer only eventually matched by McLaren after they had started talks with a 50 per cent pay cut.
"Like Lewis, I don't spend too much time on that," said Whitmarsh.
"It is what it is. I know the offer we made was higher, in a fiscal sense, than any other driver - apart from himself - is enjoying in Formula One.
"I suspect he was given a better one, but that's life."