Secretly

He secretly practiced his guitar playing in his room.

She had a secretly stashed emergency fund for unexpected expenses.

He secretly bought his wife a diamond ring for their anniversary.

The government is secretly developing a new weapon.

They secretly watched the movie from the back row.

She secretly slipped out of the room while everyone was distracted.

The company has a secretly developed product that they plan to launch next year.

She secretly watched him from behind the bushes.

The government agency conducted a secretly funded research project on mind control.