Ariana Grande and Ethan Slater are "full-on dating".

The 'Wicked' co-stars struck up a friendship while filming the big screen adaptation of the Broadway musical in the UK and started dating after their respective marriages broke down.

One source told PEOPLE: "It was obvious on the set from early on ... they were very sweet to each other and often seen laughing together.

"Everyone just thought they were both happily married though and didn’t expect them to end up dating. They are full-on dating."

The insider added that Ariana "really likes" Ethan.

Another source said that they "did not get together romantically until both were separated from their spouses".

However, an insider explained that the budding romance has been difficult for Slater's estranged wife Lilly Jay to deal with.

They married in 2018 and welcomed a son together last August but Ethan, 31, filed for divorce this week.

The source said: "They were together for so long; they met when they were in high school. They were inseparable. It’s devastating for Lilly."

Ariana, 30, split from her husband Dalton Gomez, 27, in January, following nearly two years of marriage.

The pair did not announce their split until this month.