"They started seeing each other while they were filming Spider-Man," a source tells PEOPLE of Zendaya and Tom Holland

They may just be friends in Spider-Man: Homecoming, but stars Tom Holland and Zendaya found romance in real life, a source tells PEOPLE.

“They started seeing each other while they were filming Spider-Man,” says the source. “They’ve been super careful to keep it private and out of the public eye but they’ve gone on vacations with each other and try and spend as much time as possible with one another.”

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Adds an insider: “They’re both really ambitious and they challenge each other — but, most importantly, they make each other crack up. They seem to have a really similar sense of humor and love joking around together. They have great banter back and forth.”

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Shortly before the July 7 premiere of their film, Holland, 21, opened up to PEOPLE about how Zendaya, 20, has helped him navigate the spotlight.

“We are like the best of friends. She’s so great and amazing,” Holland said of his costar. “I’m a little worried [about dealing with fame … but] Zendaya is super famous and she’s been through this and I just call her up and say, ‘How do I manage being famous?’ I’m very glad I have a friend like her.”