Hamilton's long-time confidante and right-hand woman, Cullen, wasn't just a physiotherapist - she was a pillar of support during the most successful period of the Mercedes star's career.
Over six years together, Cullen witnessed Hamilton win four consecutive drivers' championships (2017–2020), fostering a strong personal and professional bond in the process.
However, on the morning of Friday practice at the 2023 Saudi Arabian Grand Prix, news broke that she would be stepping down from her role with the seven-time champion.
It wasn't long before the motorsport world learned of her next move - a return to the racing scene, this time supporting fellow New Zealander and ex-Ferrari Academy driver Marcus Armstrong in his first full season on the IndyCar grid this year.
The Brit hasn't forgotten the impact Cullen had on his career, and he is excited to see her continue her journey within motorsport.
"I think she's a healer," Hamilton said.
"She's a positive person. Her purpose is to bring love to everyone that she meets and what she does. She's passionate about sports."
While the IndyCar paddock offers a different environment from F1, Hamilton believes Cullen's infectious enthusiasm for racing will serve her well in her new role.
"I think she's really enjoying a different environment, but still racing. I think from her time here, she became such a passionate racing fan. I think once you catch the bug, it's hard to get out of it.
"Why should she? She belongs in the sport. She's definitely very, very happy right now."
The bond forged through years of collaboration extends far beyond the confines of F1 as well.
Their friendship continues to flourish, with Hamilton even hinting at future adventures together.
"She was and still is a very good friend," he continued.
"In fact, we’re talking about getting together again and doing something together soon, like parachute jumping, maybe.
"We’ll never leave each other. I’m very grateful for everything she’s given me."